aProgram-aDay

Exception Handling in PHP

2025-10-15T00:07:00.002+05:30

Exception handling is a powerful mechanism in PHP, which is used to handle runtime errors (runtime errors are called exceptions).

The main purpose of using exception handling is to maintain the normal execution of the application.

Exception

An exception is an unexpected outcome of a program, which can be handled by the program itself.

Basically, an exception disrupts the normal flow of the program.

But it is different from an error because an exception can be handled, whereas an error cannot be handled by the program itself.

Need for Exception Handlers

Exception handling is required when an exception interrupts the normal execution of the program or application.

PHP provides a powerful mechanism for exception handling.

It can be used to handle runtime errors such as IOException, SQLException, ClassNotFoundException, and more.

A most popular example of exception handling is the divide by zero exception, which is an arithmetic exception.

Try block

The try block contains the code that may have an exception or where an exception can arise.

When an exception occurs inside the try block during runtime of code, it is caught and resolved in catch block.

The try block must be followed by a catch or finally block.

A try block can be followed by minimum one and any number of catch blocks.

Catch block

The catch block contains the code that executes when a specified exception is thrown.

It is always used with a try block, not alone.

When an exception occurs, PHP finds the matching catch block.

Throw block

t is a keyword used to throw an exception.

It also helps to list all the exceptions that a function throws but does not handle itself.

Remember that each throw must have at least one "catch".

Finally block

The finally block contains code, which is used for clean-up activity in PHP.

Basically, it executes the essential code of the program.

Exception outcome

The current state of the code is saved.

The execution of the code is switched to a predefined exception handler function.

Depending on the situation,

the handler can halt the execution of the program,
resume the execution from the saved code state,
or continue the execution of the code from another location in the code.

//Script using Exception Handler

<?php

//user-defined function with an exception

function checkNumber($num) {

if($num>=1) {

//throw an exception

throw new Exception("Value must be less than 1");

}

return true;

}

//trigger an exception in a "try" block

try {

checkNumber(5);

//If the exception throws, the below text will not be displayed

echo 'If you see this text, the passed value is less than 1';

}

//catch exception

catch (Exception $e) {

echo 'Exception Message: ' .$e->getMessage();

}

Error handling in PHP

2025-10-14T23:53:00.004+05:30

Errors

An error is a mistake in a program that may be caused by writing incorrect syntax or incorrect code.

An error message is displayed in the browser

The error message contains the filename along with the location, a message describing the error, and the line number at which the error has occurred.

Types of Errors

There are 12 unique error types, which can be grouped into 4 main categories:

Syntax Error or Parse Error
Informational (Notices)
Actionable (Warnings)
Fatal Errors

Syntax Error

It is also known as a Parse error.

These errors can occur due to common reasons like

unclosed quotes,
missing semicolon,
extra or missing parentheses,
or unclosed brackets and many more.

While compiling the program, a syntax error can be caught by the compiler.

It gives a parse error or syntax error message.

Syntax Error - Example

Example 1: Missing semicolon

<?php
/*---syntax error-------------------*/
echo "Alex: Hi! I'm Alex. </br>";
echo "Bob: I'm Bob. How are you?"
echo "Alex: I'm good! and you?";
echo "Bob: I'm also good";
?>

Parse error: syntax error, unexpected token "echo", expecting "," or ";" in C:\xampp\htdocs\Test\syntax.php on line 5

Fatal Errors

Something so terrible has happened during the execution of the script that further processing simply cannot continue.

It occurs when PHP cannot execute a critical operation, such as

calling a non-existent function
including a missing file.

These stop the script execution immediately.

Fatal Error example

<?php

function add($x, $y)

{

$sum = $x + $y;

echo "sum = " . $sum;

}

$x = 0;

$y = 20;

add($x, $y);

diff($x, $y);

Fatal error: Uncaught Error: Call to undefined function diff() in C:\xampp\htdocs\Test\fatal.php:10 Stack trace: #0 {main} thrown in C:\xampp\htdocs\Test\fatal.php on line 10

Actionable Errors (Warning Errors)

Non-fatal errors that allow the script to continue execution.

Example: Including a missing file or using an undefined variable.

Indicate that something clearly wrong has happened and that action should be taken.

e.g. file not present, database not available, missing function arguments, etc

Warning errors example

<?php

$x = "GeeksforGeeks";

include("gfg.php");

echo $x . " Computer science portal";

Warning: include(gfg.php): Failed to open stream: No such file or directory in C:\xampp\htdocs\Test\warning.php on line 3

Informational(Notice) Errors

Same as a warning error.

Harmless problem that can be avoided through the use of explicit programming.

The warning error does not stop/prevent the execution of the program.

e.g. use of an undefined variable, defining a string without quotes, etc.

Notice errors example

<?php

$x = "Notice errors are deprecated";

echo $x;

echo $error;

Warning: Undefined variable $error in C:\xampp\htdocs\Test\Notice.php on line 4

PHP Error Levels

There are 16 error levels in PHP. The 16 error levels are listed here:

E_ERROR: Fatal runtime errors.
E_WARNING: Runtime warnings (non-fatal errors).
E_PARSE: Compile-time parse errors.
E_NOTICE: Notices (non-critical runtime errors).
E_CORE_ERROR: Fatal errors during PHP's initial startup.
E_CORE_WARNING: Warnings during PHP's initial startup.
E_COMPILE_ERROR: Fatal compile-time errors.
E_COMPILE_WARNING: Compile-time warnings.
E_USER_ERROR: User-generated error messages.
E_USER_WARNING: User-generated warning messages.
E_USER_NOTICE: User-generated notice messages.
E_STRICT: Suggestions for improving code compatibility.
E_RECOVERABLE_ERROR: Catchable fatal errors.
E_DEPRECATED: Notices for deprecated code.
E_USER_DEPRECATED: User-generated deprecation warnings.
E_ALL: Represents all errors and warnings (except E_STRICT in older PHP versions).

Causing (Triggering) errors

It is possible to cause errors in PHP at any point in your script.

The trigger_error( ) function takes two parameters:

the string output message to be printed out as the error
and an optional second parameter of the type of error

trigger_error($msg,$type);

e.g.

…

if (!$db_conn) {

trigger_error(‘db conn failed’,E_USER_ERROR);

}

trigger_error( ) is better than just printing an error message and exiting the script

trigger_error( ) takes the form of PHP’s default errors

—it will automatically print out the filename and line number where the error occurred.

The second parameter affects how the script should react to the error.

If the second parameter is not provided, the default is a user notice—a minor message that many people might not even see.

However, any error type can be given as the second parameter, which can halt the execution of the script if the error is triggered.

Customising Error Handling

Generally, how PHP handles errors is defined by various constants in the installation (php.ini).

1. Set error reporting settings

2. Suppressing Errors

3. Custom Error Handler

1. Set error reporting settings

error_reporting($level)

This function can be used to control which errors are displayed and which are simply ignored.

The $level is an optional parameter

The effect only lasts for the duration of the execution of your script.

<?php

// Turn off all error reporting

error_reporting(0);

// Report simple running errors

error_reporting(E_ERROR | E_WARNING | E_PARSE);

// Reporting E_NOTICE (to report uninitialized variables or catch variable name misspellings ...)

error_reporting(E_ERROR | E_WARNING | E_PARSE | E_NOTICE);

// Report all errors except E_NOTICE

error_reporting(E_ALL ^ E_NOTICE);

// Report ALL PHP errors

error_reporting(E_ALL);

Note: Hiding errors is NOT a solution to a problem.

2. Suppressing Errors

The special @ operator can be used to suppress function errors.

Any error produced by the function is suppressed and not displayed by PHP, regardless of the error reporting setting

PHP supports one error control operator: the at sign (@). When prepended to an expression in PHP, any diagnostic error that might be generated by that expression will be suppressed.

<?php

$my_file = @file ('non_existent_file') or

die ("Failed opening file: error was '" . error_get_last()['message'] . "'");

Note: Error suppression is NOT a solution to a problem.

It can be useful to locally define your own error-handling mechanisms.

If you suppress any errors, you must check for them yourself elsewhere.

3. Custom Error Handler

function err_handler($errcode,$errmsg,$file,$lineno)

{

echo ‘An error has occurred!<br />’;

echo “file: $file<br />”;

echo “line: $lineno<br />”;

echo “Problem: $errmsg”;

return true;

}

The function then needs to be registered as your custom error handler:

set_error_handler(‘err_handler’);

You can ‘mask’ the custom error handler so it only receives certain types of errors. e.g. to register a custom handler just for user-triggered errors:

set_error_handler(‘err_handler’,E_USER_NOTICE | E_USER_WARNING | E_USER_ERROR);

A custom error handler is never passed E_PARSE, E_CORE_ERROR or E_COMPILE_ERROR errors as these are considered too dangerous.

Often used in conjunction with a ‘debug’ flag for a neat combination of debug and production code display..

PHP Study Material

2025-10-14T22:48:00.002+05:30

SWING COMPONENTS

2025-10-14T22:31:00.006+05:30

The Swing components offer rich functionality and enable high-level customisation. The following components are described in this section.

JLabel
JTextField
JButton
JToggleButton
JCheckBox
JRadioButton
JTabbedPane
JScrollPane
JList
JComboBox
JTree
JTable

JLabel

JLabel is Swing’s easiest-to-use component.

JLabel can be used to display text and/or an icon.

JLabel defines several constructors. Here are three of them:

JLabel(Icon icon)
JLabel(String str)
JLabel(String str, Icon icon, int align)

The align argument specifies the horizontal alignment of the text and/or icon within the label. It must be one of the following values: LEFT, RIGHT, CENTER, LEADING, or TRAILING.

The easiest way to obtain an icon is to use the ImageIcon class. An object of type ImageIcon can be passed as an argument to the Icon parameter of JLabel’s constructor.

Methods in JLabel

The icon and text associated with the label can be obtained by the following methods:

Icon getIcon( )

String getText( )

The icon and text associated with a label can be set by these methods:

void setIcon(Icon icon)

void setText(String str)

Program using JLabel

import java.awt.*;

import javax.swing.*;

public class MyFrame extends JFrame

{

JLabel l;

MyFrame()

{

setSize(500, 300);

setTitle("My Application");

setLayout(new FlowLayout());

l = new JLabel("This is a label!");

add(l);

setVisible(true);

setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

}

public static void main(String[] args)

{

MyFrame mf = new MyFrame();

}

JTextField

JTextField is the simplest and most widely used Swing text component. JTextField allows you to edit one line of text. It is derived from JTextComponent. Three of JTextField’s constructors are shown here:

JTextField(int cols)
JTextField(String str, int cols)
JTextField(String str)

Here, str is the string to be initially presented, and cols is the number of columns in the text field.

If no string is specified, the text field is initially empty.

Events handled in JTextField

ActionEvent - when the user presses the Enter key

CaretEvent - each time the cursor changes position

Methods in JTextField

setText() - to display text

getText() - to retrieve text from the text field

Program using JTextField

import java.awt.*;

import javax.swing.*;

public class MyFrame extends JFrame

{

JTextField jtf;

MyFrame()

{

setSize(500, 300);

setTitle("My Application");

setLayout(new FlowLayout());

jtf = new JTextField(20);

add(jtf);

setVisible(true);

setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

}

public static void main(String[] args)

{

MyFrame mf = new MyFrame();

}

Swing Buttons

Swing defines four types of buttons: JButton, JToggleButton, JCheckBox, and JRadioButton.

A button generates an action event when it is pressed.

JButton

The JButton class provides the functionality of a push button. Three of its constructors are shown here:

JButton(Icon icon)
JButton(String str)
JButton(String str, Icon icon)

When the button is pressed, an ActionEvent is generated.

getActionCommand() - used to identify the button pressed when two or more buttons are present.

Program using JButton

import java.awt.*;

import javax.swing.*;

public class MyFrame extends JFrame

{

JButton b;

MyFrame()

{

setSize(500, 300);

setTitle("My Application");

setLayout(new FlowLayout());

b = new JButton("Click Me");

add(b);

setVisible(true);

setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

}

public static void main(String[] args)

{

MyFrame mf = new MyFrame();

}

JToggleButton

A toggle button looks just like a push button, but it acts differently because it has two states: pushed and released. JToggleButton defines several constructors. The most commonly used one is:

JToggleButton(String str)

JToggleButton generates an action event each time it is pressed.

JToggleButton also generates an item event.

When a JToggleButton is pressed, it is selected. When it is popped out, it is deselected.
To handle ItemEvent, the ItemListener interface is implemented. This interface provides itemStateChanged() method. Inside itemStateChanged( ),

getItem( ) - method can be used to identify the item selected.

isSelected() - used to check whether an item is selected or not.

Program using JToggleButton

import java.awt.*;

import javax.swing.*;

public class MyFrame extends JFrame

{

JToggleButton b;

MyFrame()

{

setSize(500, 300);

setTitle("My Application");

setLayout(new FlowLayout());

b = new JToggleButton("Click Me");

add(b);

setVisible(true);

setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

}

public static void main(String[] args)

{

MyFrame mf = new MyFrame();

}

Check Boxes

The JCheckBox class provides the functionality of a check box. JCheckBox defines several constructors. The one used here is

JCheckBox(String str)

When the user selects or deselects a check box, an ItemEvent is generated.

A call to isSelected( ) determines if the box was selected or cleared. The getText( ) method gets the text for that check box.

Program using JCheckBox

import java.awt.*;

import javax.swing.*;

public class MyFrame extends JFrame

{

JCheckBox c1;

JCheckBox c2;

JCheckBox c3;

MyFrame()

{

setSize(500, 300);

setTitle("My Application");

setLayout(new FlowLayout());

c1 = new JCheckBox("C");

c2 = new JCheckBox("C++");

c3 = new JCheckBox("Java");

add(c1);

add(c2);

add(c3);

setVisible(true);

setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

}

public static void main(String[] args)

{

MyFrame mf = new MyFrame();

}

Radio Buttons

Radio buttons are a group of mutually exclusive buttons, where only one button can be selected at any time. They are supported by the JRadioButton class, which extends JToggleButton. JRadioButton provides several constructors.

JRadioButton(String str)

In order for their mutually exclusive nature to be activated, radio buttons must be configured into a group. Only one of the buttons in the group can be selected at any time. A button group is created by the ButtonGroup class. Elements are then added to the button group via the following method:

void add(AbstractButton ab)

Methods

getActionCommand() - returns the label of the radio button

isSelected() - used to check whether a radio button is selected

getSource() - used to identify the radio button pressed

Program using JRadioButton

import java.awt.*;

import javax.swing.*;

public class MyFrame extends JFrame

{

JRadioButton r1;

JRadioButton r2;

ButtonGroup bg;

MyFrame()

{

setSize(500, 300);

setTitle("My Application");

setLayout(new FlowLayout());

r1 = new JRadioButton("Male");

r2 = new JRadioButton("Female");

add(r1);

add(r2);

bg = new ButtonGroup();

bg.add(r1);

bg.add(r2);

setVisible(true);

setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

}

public static void main(String[] args)

{

MyFrame mf = new MyFrame();

}

JTabbedPane

Tabbed panes are very common in the modern GUI. It manages a set of components by linking them with tabs. Selecting a tab causes the component associated with that tab to come to the forefront. JTabbedPane defines three constructors.

JTabbedPane()

JTabbedPane(int tabPlacement)

After creating a TabbedPane object, tabs are added using the following method:

void addTab(String name, Component comp)

The general procedure to use a tabbed pane is outlined here:

Create an instance of JTabbedPane.
Add each tab by calling addTab( ).
Add the tabbed pane to the content pane

Program Using JTabbedPane

import java.awt.*;

import javax.swing.*;
public class MyFrame extends JFrame
{
JCheckBox c1;
JCheckBox c2;
JCheckBox c3;
JRadioButton r1;
JRadioButton r2;
ButtonGroup bg;
JLabel l;
JTextField jtf;
JPanel langs;
JPanel gender;
JPanel name;
JTabbedPane jtp;
MyFrame()
{
setSize(500, 300);
setTitle("My Application");
setLayout(new FlowLayout());
c1 = new JCheckBox("C");
c2 = new JCheckBox("C++");
c3 = new JCheckBox("Java");
langs = new JPanel();
langs.add(c1);
langs.add(c2);
langs.add(c3);
r1 = new JRadioButton("Male");
r2 = new JRadioButton("Female");
bg = new ButtonGroup();
bg.add(r1);
bg.add(r2);
gender = new JPanel();
gender.add(r1);
gender.add(r2);
l = new JLabel("Enter Name: ");
jtf = new JTextField(20);
name = new JPanel();
name.add(l);
name.add(jtf);
jtp = new JTabbedPane();
jtp.addTab("Languages", langs);
jtp.addTab("Gender", gender);
jtp.addTab("Name", name);
add(jtp);
setVisible(true);
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
}
public static void main(String[] args)
{
MyFrame mf = new MyFrame();
}
}

JScrollPane

JScrollPane is a lightweight container that automatically handles the scrolling of another component. The component being scrolled can be either an individual component or a group of components. In either case, if the object being scrolled is larger than the viewable area, horizontal and/or vertical scroll bars are automatically provided.

The viewable area of a scroll pane is called the viewport. It is a window in which the component being scrolled is displayed. The scroll bars scroll the component through the viewport. A JScrollPane will dynamically add or remove a scroll bar as needed. JScrollPane defines several constructors. The simplest one is hown here:

JScrollPane(Component comp)

Here are the steps to follow to use a scroll pane:

Create the component to be scrolled.
Create an instance of JScrollPane, passing to it the object to scroll.
Add the scroll pane to the content pane

Program using JScrollPane

import javax.swing.*;

public class JScrollPaneExample
{
    public static void main(String[] args)
    {
        // Create a JFrame
        JFrame frame = new JFrame("JScrollPane Example");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setSize(400, 300);

        // Create a JTextArea
        JTextArea textArea = new JTextArea(10, 30);
        textArea.setText("This is a sample text.
                          \nYou can add more lines to see the scroll effect.
                          \nKeep typing to test scrolling!");

        // Wrap the JTextArea inside a JScrollPane
        JScrollPane scrollPane = new JScrollPane(textArea);

        // Add the JScrollPane to the frame
        frame.add(scrollPane);
   // Make the frame visible
        frame.setVisible(true);
    }
}

JList

In Swing, the basic list class is called JList. It supports the selection of one or more items from a list..

JList provides several constructors. The one used here is

JList(E[ ] items)

JList is based on two models. The first is ListModel. This interface defines how access to the list data is achieved. The second model is the ListSelectionModel interface, which defines methods that determine what list item or items are selected.

A JList generates a ListSelectionEvent when the user makes or changes a selection. It is handled by implementing ListSelectionListener. This listener specifies only one method, called valueChanged( ),

By default, a JList allows the user to select multiple ranges of items within the list. The method

void setSelectionMode(int mode)

is used to change the selection mode. It must be one of these values defined by ListSelectionModel: SINGLE_SELECTION

SINGLE_INTERVAL_SELECTION

MULTIPLE_INTERVAL_SELECTION

Methods to get the selected items

int getSelectedIndex( )

Indexing begins at zero. So, if the first item is selected, this method will return 0. If no item is selected, –1 is returned.

getSelectedValue( )

It returns a reference to the first selected value. If no value has been selected, it returns null.

Program using JList

import java.awt.*;

import javax.swing.*;
public class MyFrame extends JFrame
{
JList<String> jl;
JScrollPane jsp;
MyFrame()
{
setSize(500, 300);
setTitle("My Application");
setLayout(new FlowLayout());
String[] branches = {"CSE", "ECE", "EEE", "IT", "MECH", "CIV"};
jl = new JList<String>(branches);
jsp = new JScrollPane(jl);
jsp.setPreferredSize(new Dimension(120, 80));
add(jsp);
setVisible(true);
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
}
public static void main(String[] args)
{
MyFrame mf = new MyFrame();
}
}

JComboBox

A combo box (a combination of a text field and a drop-down list)

A combo box displays one entry, but it will also display a drop-down list that allows a user to select a different entry.

The JComboBox constructor used by the example is shown here:

JComboBox(E[ ] items)

Items can be dynamically added to the list of choices via the addItem( ) method, shown here:

void addItem(E obj)

JComboBox generates an

action event when the user selects an item from the list.

item event - when the state of selection changes, which occurs when an item is selected or deselected.

getSelectedItem( ) - to obtain the item selected in the list

Program using JComboBox

import java.awt.*;

import javax.swing.*;

public class MyFrame extends JFrame

{

JComboBox<String> jc;

MyFrame()

{

setSize(500, 300);

setTitle("My Application");

setLayout(new FlowLayout());

String[] branches = {"CSE", "ECE", "EEE", "IT", "MECH", "CIV"};

jc = new JComboBox<String>(branches);

add(jc);

setVisible(true);

setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

}

public static void main(String[] args)

{

MyFrame mf = new MyFrame();

}

Trees

A tree is a component that presents a hierarchical view of data. Trees are implemented in Swing by the JTree class. A sampling of its constructors is shown here:

JTree(Object[ ] obj)
JTree(Vector v)
JTree(TreeNode tn)

Although JTree is packaged in javax.swing, its support classes and interfaces are packaged in javax.swing.tree.

JTree relies on two models: TreeModel and TreeSelectionModel.

Events generated

TreeExpansionEvent events occur when a node is expanded or collapsed.

TreeSelectionEvent is generated when the user selects or deselects a node within the tree.

TreeModelEvent is fired when the data or structure of the tree changes.

The listeners for these events are TreeExpansionListener, TreeSelectionListener, and TreeModelListener, respectively. The tree event classes and listener interfaces are packaged in javax.swing.event.

Here are the steps to follow to use a tree:

Create an instance of JTree.
Create a JScrollPane and specify the tree as the object to be scrolled.
Add the scroll pane to the content pane.

Program using JTree

import javax.swing.*;

import javax.swing.tree.DefaultMutableTreeNode;

public class SimpleJTreeExample {

public static void main(String[] args) {

// Create the root node

DefaultMutableTreeNode root = new DefaultMutableTreeNode("Root");

// Add child nodes

DefaultMutableTreeNode child1 = new DefaultMutableTreeNode("Child 1");

DefaultMutableTreeNode child2 = new DefaultMutableTreeNode("Child 2");

root.add(child1);

root.add(child2);

// Add sub-child nodes

child1.add(new DefaultMutableTreeNode("Sub-child 1.1"));

child1.add(new DefaultMutableTreeNode("Sub-child 1.2"));

child2.add(new DefaultMutableTreeNode("Sub-child 2.1"));

// Create the JTree

JTree tree = new JTree(root);

// Add the tree to a scroll pane

JScrollPane treeView = new JScrollPane(tree);

// Create a JFrame to display the tree

JFrame frame = new JFrame("Simple JTree Example");

frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

frame.add(treeView);

frame.setSize(300, 300);

frame.setVisible(true);

}

JTable

JTable is a component that displays rows and columns of data. It is also possible to select a row, column, or cell within the table, and to change the data within a cell. JTable has many classes and interfaces associated with it. These are packaged in javax.swing.table.

JTable supplies several constructors. The one used here is

JTable(Object[ ][ ] data, Object[ ] colHeads).

Here, data is a two-dimensional array of the information to be presented, and colHeads is a one-dimensional array with the column headings.

JTable relies on three models.

TableModel - defines those things related to displaying data in a two-dimensional format

TableColumnModel - defines a table in terms of columns

ListSelectionModel - determines how items are selected in the table

A JTable can generate several different events.

ListSelectionEvent is generated when the user selects something in the table

TableModelEvent is fired when that table’s data changes in some way

Here are the steps required to set up a simple JTable that can be used to display data:

Create an instance of JTable.

Create a JScrollPane object, specifying the table as the object to scroll.

Add the scroll pane to the content pane.

Program using JTable

import java.awt.*;

import javax.swing.*;

public class MyFrame extends JFrame

{

JTable jt;

JScrollPane jsp;

MyFrame()

{

setSize(500, 300);

setTitle("My Application");

setLayout(new FlowLayout());

String[] colHeads = {"Student", "JP", "FLAT", "CO"};

String[][] data = { {"Ramesh", "77", "80", "75"},

{"Suresh", "89", "86", "83"},

{"Mahesh", "74", "80", "75"},

{"Dinesh", "78", "80", "75"},

{"Gireesh", "89", "86", "83"},

{"Paramesh", "77", "84", "72"} };

jt = new JTable(data, colHeads);

jsp = new JScrollPane(jt);

jsp.setPreferredSize(new Dimension(450, 100));

add(jsp);

setVisible(true);

setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

}

public static void main(String[] args)

{

MyFrame mf = new MyFrame();

}

Swings in Java

2025-10-14T19:52:00.005+05:30

ORIGIN OF SWING

The AWT defines a basic set of controls, windows, and dialog boxes that support a usable, but limited, graphical interface.
The solution was Swing. Introduced in 1997,
Swing was included as part of the Java Foundation Classes (JFC).
Swing was initially available for use with Java 1.1 as a separate library.
However, beginning with Java 1.2, Swing (and the rest of the JFC) was fully integrated into Java.
The Java Swing tutorial is part of the Java Foundation Classes (JFC), which is used to create window-based applications.
It is built on top of the AWT (Abstract Windowing Toolkit) API and entirely written in Java.
The javax.swing package provides classes for java swing API, such as JButton, JTextField, JTextArea, JRadioButton, JCheckBox, JMenu, JColorChooser, etc.

‌FEATURES OF SWINGS

‌Lightweight Components:

The components created using the swings package don’t need the help of the native operating system.
Swings is part of Java Foundation Classes (JFC), which are purely developed in Java.
Swing components require fewer memory and CPU cycles than AWT components.
Hence, swing components are lightweight components.

Pluggable Look and Feel:

Swings supports pluggable look and feel, i.e., the appearance of a component can be separated from the component's behaviour.
This enables programmers to assign different looks (themes) for the same component without changing its behaviour.

‌SWING VS AWT

‌MODEL VIEW CONTROLLER (MVC) ARCHITECTURE

‌Every GUI control or component contains three aspects:

The way the component looks (appearance) when rendered on the screen.
The way the component reacts to the user.
The state information associated with the component.

‌In MVC terminology, the model corresponds to the state information of a component.

For example, a button might contain a field that represents whether it is pressed or released.

The view corresponds to the look or appearance of the component when rendered on the screen.

For example, a button is displayed as a rectangle.

The controller determines how the component reacts to the user events.

For example, when the user presses a button, a new frame can be displayed.

‌MODEL-DELEGATE ARCHITECTURE

‌Swing uses a modified version of MVC that combines the view and the controller into a single logical entity called the UI delegate.
For this reason, Swing’s approach is called either the Model-Delegate architecture or the Separable Model architecture.
Swing’s pluggable look and feel is made possible by its Model-Delegate architecture.
To support the Model-Delegate architecture, most Swing components contain two objects.

The first represents the model.
The second represents the UI delegate.

‌COMPONENTS AND CONTAINERS

‌A Swing GUI consists of two key items: components and containers.
A component is an independent visual control, such as a push button or slider.
A container holds a group of components.
Thus, a container is a special type of component designed to hold other components.
For a component to be displayed, it must be held within a Container.
Thus, all Swing GUIs will have at least one container

‌COMPONENTS

‌Swing components are derived from the class JComponent (except the four top-level containers).
JComponent supports pluggable look and feel and supports the functionality common to all components.
JComponent class inherits the AWT classes Container and Component.
All of Swing’s components are represented by classes defined within the package javax.swing.

‌COMPONENTS IN SWINGS

‌CONTAINERS

‌Swing defines two types of containers.
The first are top-level containers: JFrame, JApplet, JWindow, and JDialog.

The top-level containers are heavyweight since they are inherited from the AWT classes Component and Container.
A top-level container is not contained within any other container.
The one most commonly used for applications is JFrame.

The second type of containers supported by Swing are lightweight containers.

Lightweight containers do inherit JComponent.
An example of a lightweight container is JPanel
In the past, the one used for applets was JApplet.

‌EVENT HANDLING IN SWINGS

‌The event handling mechanism used by Swing is the same as that used by the AWT.
This approach is called the delegation event model.
Swing uses the same events as does the AWT, and these events are packaged in java.awt.event.
Events specific to Swing are stored in javax.swing.event.

‌PAINTING IN SWING

‌To write output directly to the surface of a component, one or more drawing methods defined by the AWT, such as drawLine( ) or drawRect( ) must be used.
The AWT class Component defines a method called paint( ) that is used to draw output directly to the surface of a component.
Because JComponent inherits Component, all Swing’s lightweight components inherit the paint( ) method.
Swing uses three distinct methods: paintComponent( ), paintBorder( ), and paintChildren( ).
These methods paint the indicated portion of a component and divide the painting process into its three distinct, logical actions.
To paint to the surface of a Swing component, create a subclass of the component class and then override its paintComponent( ) method.

Simple Swing Program

import java.awt.*;

import java.awt.event.*;

import javax.swing.*;

class EventDemo

{

JLabel jlab;

EventDemo()

{

// Create a new JFrame container.

JFrame jfrm = new JFrame("An Event Example");

// Specify FlowLayout for the layout manager.

jfrm.setLayout(new FlowLayout());

// Give the frame an initial size.

jfrm.setSize(720, 690);

// Terminate the program when the close button is pressed

jfrm.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

// Make three buttons.

JButton b1 = new JButton("RED");

JButton b2 = new JButton("BLUE");

JButton b3 = new JButton("GREEN");

// Add action listener for red.

b1.addActionListener(new ActionListener()

{

public void actionPerformed(ActionEvent ae)

{

jfrm.getContentPane().setBackground(Color.red);

}

});

// Add action listener for blue.

b2.addActionListener(new ActionListener()

{

public void actionPerformed(ActionEvent ae)

{

jfrm.getContentPane().setBackground(Color.blue);

}

});

//Add action listener for green

b3.addActionListener(new ActionListener()

{

public void actionPerformed(ActionEvent ae)

{

jfrm.getContentPane().setBackground(Color.green);

}

});

// Add the buttons to the content pane.

jfrm.add(b1);

jfrm.add(b2);

jfrm.add(b3);

// Create a text-based label.

JLabel jlab = new JLabel("Press a button.");

// Add the label to the content pane.

jfrm.add(jlab);

// Display the frame.

jfrm.setVisible(true);

}

public static void main(String args[])

{

SwingUtilities.invokeLater(new Runnable()

{

public void run()

{

new EventDemo();

}

});

}

Applets in Java

2025-10-10T04:29:00.000+05:30

Introduction to Applets

Applets are small applications that are

accessed on an Internet server,
transported over the Internet,
Automatically installed,
and run as part of a web document

An applet is a Java program that runs in a Web browser. They can be executed by browsers on multiple platforms like Windows, Linux, and Mac. They can be executed by browsers on various platforms, including Windows, Linux, and macOS.

Java can be used to create two types of programs: applications and applets.

Applet Vs Application Programs

Applet	Application
It is initialised through init().	Starts its execution through the main() method
It is a small program that uses another application (browser) program for its execution.	An application is a program executed on a computer independently.
Cannot run independently, requires API's	Can run alone but requires JRE.
Prior installation is not needed. Browsers with an applet plug-in are enough.	Requires prior explicit installation on the local computer.
The files cannot be read or written on the local computer through the applet.	Applications are capable of performing those operations on the files on the local computer.
Requires security for the system as the applets are untrusted.	No security concerns exist.
Created by extending the Applet class	User-defined class with main()
Uses a GUI interface to interact with users	Uses I/O stream classes

Sample Applet Program

import java. awt.*;

import java.applet.*;

public class MyApplet extends Applet

{

public void paint(Graphics g)

{

g.drawString("Hello World!", 20, 20);

}

/*<applet code="MyApplet" height="300" width="500">

</applet>*/

There are two ways to run an applet:

Executing the applet within a Java-compatible Web browser, such as Netscape Navigator.
Using an applet viewer, such as the standard JDK tool, appletviewer.

An appletviewer executes the applet in a window. This is generally the fastest and easiest way to test an applet.

To execute an applet in a Web browser, it is essential to write a short HTML text file that contains the appropriate APPLET tag.

</applet>

This tag can also be embedded within a Java file inside a comment line.

Applet begins with two import statements.

The first imports the Abstract Window Toolkit (AWT) classes.

The second import statement imports the applet package, which contains the class Applet

Every AWT-based applet must be a subclass (either directly or indirectly) of Applet.

The class SimpleApplet must be declared as public, because it will be accessed by code that is outside the program.

Life Cycle of an Applet

An applet's life cycle includes the following methods

init( )
start( )
paint( )
stop( )
destroy( )

When an applet begins, the AWT calls the following methods, in this sequence:

init( )
start( )
paint( )

When an applet is terminated, the following sequence of method calls takes place:

stop( )
destroy( )

init() and start() methods

The init( ) method is the first method to be called.

This is where the variables are initialised.

init( ) is called once—the first time an applet is loaded

The start( ) method is called after init( ).

start( ) is called each time an applet's HTML document is displayed on screen.

So, if a user leaves a web page and comes back, the applet resumes execution at start( ).

paint() method

The paint( ) method is called each time the applet's output must be redrawn.

paint( ) is also called when the applet begins execution.

The paint( ) method has one parameter of type Graphics.

This parameter will contain the graphics context, which describes the graphics environment in which the applet is running.

This context is used whenever output to the applet is required.

stop() and destroy()

The stop( ) method is called when a web browser leaves the HTML document containing the applet.

Applet uses stop( ) to suspend threads that don't need to run when the applet is not visible.

The destroy( ) method is called when the environment determines that the applet needs to be removed from memory.

The stop( ) method is always called before destroy( ).

repaint() and update()

The paint () method is called automatically by the browser whenever the applet window needs to be redrawn.

The user can call the repaint() method whenever the applet window needs to be redrawn.

The repaint () method will call the update () method of the Component class, which clears the window with the background colour of the applet and then calls the paint () method.

Types of Applets

Applets are of two types

Simple applets
JApplets

Simple applets can be created by extending Applet class

These applets use the Abstract Window Toolkit (AWT) to provide the graphical user interface.

This style of applet has been available since Java was first created.

JApplets can be created by extending JApplet class of javax.swing package

Simple display methods in Applets

void drawString(String message, int x, int y); //To display text on the applet window

void setBackground(Color newColor) //To set the background colour of the applet window

void setForeground(Color newColor) //To set colour to the text and other components on the applet

setBackground(Color.green);

setForeground(Color.red);

Status Window

An applet can also output a message to the status window of the browser or applet viewer on which it is running.

To do so, call showStatus( ) with the string to be displayed.

The HTML APPLET tag

< APPLET

[CODEBASE = codebaseURL]

CODE = appletFile

[ALT = alternateText]

[NAME = appletInstanceName]

WIDTH = pixels HEIGHT = pixels

[ALIGN = alignment]

[VSPACE = pixels] [HSPACE = pixels]

[< PARAM NAME = AttributeName VALUE = AttributeValue>]

[< PARAM NAME = AttributeName2 VALUE = AttributeValue>]

Document Base – Filename from where the Java file containing the applet tag is loaded

Code Base – directory where the applet class file resides

Passing parameters to Applets

Parameters specify extra information that can be passed to an applet from the HTML page.

Parameters are specified using the HTML’s param tag.

The < APPLET> tag in HTML is used to pass parameters to an applet.

Param tag

The <param> tag is a subtag of the <applet> tag.

The <param> tag contains two

attributes: name and value

which are used to specify the name of the parameter and its value, respectively.

For example, the param tags for passing name and age parameters

getParameter() method

The getParameter() method of the Applet class can be used to retrieve the parameters passed from the HTML page.

The syntax of the getParameter() method is as follows:

String getParameter(String param-name)

Program using the param tag

import java. awt.*;

import java.applet.*;

public class MyApplet extends Applet

{

String n;

String a;

public void init()

{

n = getParameter("name");

a = getParameter("age");

}

public void paint(Graphics g)

{

g.drawString("Name is: " + n, 20, 20);

g.drawString("Age is: " + a, 20, 40);

}

</applet>

Graphics Package

Graphics belongs to a package named java. awt

import java.awt.Graphics;

To use Graphics, the above line must be placed at the very top of the applet program, before the public class header.

The window coordinate system

Each (x, y) position is a pixel ("picture element").

Position (0, 0) is at the window's top-left corner.

x increases rightward and y increases downward.

The rectangle from (0, 0) to (200, 100) looks like this:

Graphics Methods

Method name	Description
g.drawLine(x1, y1, x2, y2);	line between points (x1, y1), (x2, y2)
g.drawOval(x, y, width, height);	Outline the largest oval that fits in a box of size width * height, with top-left at (x, y)
g.drawRect(x, y, width, height);	outline of a rectangle of size width * height with top-left at (x, y)
g.drawString(text, x, y);	text with bottom-left at (x, y)
g.fillOval(x, y, width, height);	fill the largest oval that fits in a box of size width * height with top-left at (x, y)
g.fillRect(x, y, width, height);	fill rectangle of size width * height with top-left at (x, y)
g.setColor(Color);	Set Graphics to paint any following shapes in the given colour

Inner Classes in Java

2025-10-01T18:59:00.003+05:30

A class can be defined inside another class. Such classes are called nested classes.

The nested class is like a member of the enclosing class. The enclosing class cannot access the members of the nested class directly. But the nested class can access all the members of the enclosing class, including the private members.

For example,

In the above figure, class B is nested inside class A. Class B is a member of Class A and can access all its members directly. But class A cannot access the members of class B.

There are two types of nested classes: static and non-static.

Static nested class

The static nested class is declared with a static modifier. It can access only the static members of the enclosing class. It does not have access to the non-static members of the outer class.

class Outer

{

static class Inner

{

public static void display()

{

System.out.println("inside inner class Method");

}

public class Main

{

public static void main(String[] args)

{

Outer.Inner.display();

}

Non-static nested class / Inner class

An inner class is a non-static nested class. It can access all the variables and methods of the outer class, including the private members, directly. Members of the inner class are known only within the scope of the inner class and may not be used by the outer class.

// Demonstrate an inner class.

class Outer

{

int outer_x = 100;

void test()

{

Inner inner = new Inner();

inner.display();

}

// this is an inner class

class Inner

{

void display()

{

System.out.println("display: outer_x = " + outer_x);

}

class InnerClassDemo

{

public static void main(String[] args)

{

Outer outer = new Outer();

outer.test();

}

Advantages of Inner Class

Encapsulation: Inner classes can access private members of the outer class, improving encapsulation.

Code Organisation: They group related logic, making the code more modular and easier to maintain.

Polymorphism: Inner classes can implement polymorphic behavior by extending or implementing different classes/interfaces.

Callbacks: Useful for event-driven programming, such as defining callback functions.

Inner classes are a powerful feature in Java, enabling better design and modularity in object-oriented programming.

Steps to create Packages in Java

2025-08-29T13:16:00.004+05:30

Here are the steps to create a package in Java:

1. Define the Package

Use the package keyword at the very top of the Java file.
Example:
```
package mypackage;
```

2. Organize Your Files

Create a sub directory in the current directory with a name that matches the package name.
For example, if your package is mypackage, create a folder named mypackage.

3. Write Your Java Class

Save your Java file inside the corresponding folder.

Example:

package mypackage;

public class MyClass {
    public void displayMessage() {
        System.out.println("Hello from MyClass in mypackage!");
    }
}

4. Compile the Package

After saving the file, move to the parent directory by entering cd.. at the command prompt.
Navigate to the parent directory of the package folder in the terminal/command prompt.
Use the javac command to compile the file:
```
javac mypackage/MyClass.java
```

5. Use the Package

To use the package in another Java file, import it using the import statement.

Example:

import mypackage.MyClass;

public class Main {
    public static void main(String[] args) {
        MyClass obj = new MyClass();
        obj.displayMessage();
    }
}

Benefits of Using Packages

Organizes your code.
Avoids naming conflicts.
Provides access control.

Let me know if you'd like further clarification! 😊

Student dtd

2024-12-09T12:16:00.006+05:30

<!ELEMENT courses (student)+>

<!ELEMENT student (name,regno)>

<!ATTLIST student class (UG|PG) FIXED "UG">

<!ELEMENT name (first,last)>

<!ELEMENT first (#PCDATA)>

<!ELEMENT last (#PCDATA)>

<!ELEMENT regno (#PCDATA)>

Bootstrap working with content

2024-04-02T23:15:00.001+05:30

‌WORKING WITH CONTENT

‌Content components in Bootstrap are reserved for the most commonly used HTML elements such as images, tables, typography, and more.
Bootstrap comes with a brand-new CSS reset called Reboot.
It builds on top of Normalize.css to make your site look even better out of the box.
Reboot, a collection of element-specific CSS changes in a single file, kickstart Bootstrap to provide an elegant, consistent, and simple baseline to build upon.

‌REBOOT BASICS

‌Update some browser default values to use rems instead of ems for scalable component spacing.
rem is short for root em and is a little bit different from a regular em unit.
em is a relative unit to the font-size of the parent element it is contained within.
The rem unit is not relative to its parent, it is relative to the root or HTML element.
This makes it much easier to determine the actual size of text or other content components that will appear on the screen.

‌REBOOT PAGE DEFAULTS

‌The <html> and <body> elements are updated to provide better page-wide defaults
The box-sizing is globally set on every element—including *::before and *::after, to border-box.
The base font-size is set to 16px (the browser default).
font-size: 1rem is applied on the <body> for easy responsive type-scaling via media queries
The <body> also sets a global font-family, font-weight, line-height, and color. This is inherited later by some form elements to prevent font inconsistencies.
For safety, the <body> has a declared background-color, defaulting to #fff.

‌REBOOT HEADINGS AND PARAGRAPHS

‌All heading elements have been reset to have their top-margin removed.
Headings have a margin-bottom value of 0.5rem
Paragraphs have a margin-bottom value of 1rem.
Headings inherit their color by default, but can be overridden using CSS variable, --bs-heading-color.

Lists
All lists have their top margin removed, has a bottom margin of 1rem.
In nesting lists, there is no bottom-margin at all.
The left padding has also been reset

‌REBOOT TABLES AND FORMS

‌Tables are slightly adjusted to style <caption>s, collapse borders, and ensure consistent text-align throughout.

Various form elements have been rebooted for simpler base styles.
<fieldset>s have no borders, padding, or margin so they can be easily used as wrappers for individual inputs or groups of inputs.
<legend>s, like fieldsets, have also been restyled to be displayed as a heading of sorts.
<label>s are set to display: inline-block to allow margin to be applied.
<input>s, <select>s, <textarea>s, and <button>s are mostly addressed by Normalize, but Reboot removes their margin and sets line-height: inherit, too.
<textarea>s are modified to only be resizable vertically as horizontal resizing often “breaks” page layout.
<button>s and <input> button elements have cursor: pointer when :not(:disabled).

‌HEADINGS EXAMPLE

‌<h1 class="display-1">Display 1</h1>
<h1 class="display-2">Display 2</h1>
<h1 class="display-3">Display 3</h1>
<h1 class="display-4">Display 4</h1>
<h3>
This is the main title
<small class="text-muted">this is a description</small>
</h3>

Display headings are configured via the $display-font-sizes Sass map and two variables, $display-font-weight and $display-line-height.

‌PARAGRAPH EXAMPLE

‌<p class="lead"> here's some text with the .lead class to make this paragraph look a bit different and standout. </p>
TEXT FORMATTING
<p>mark tag <mark>highlights</mark> text.</p>

<p>del tag used to <del>delete</del> text.</p>

<p>s tag is used for text which is <s>no longer accurate</s>.</p> <p><ins>This line is added.</ins></p>

<p>This is <u>underlined</u>.</p>

<p><small>small tag is used for fine prints.</small></p>

<p><strong>strong tag is used to bold text.</strong></p>

<p><em>em tag is used to italicize text.</em></p>

‌LISTS

‌Unstyled class
Remove the default list-style and left margin on list items
This only applies to immediate children list items
Example
<ul class="list-unstyled"> <li>item</li> <li>item</li> <li>item</li> <li>item</li> <li>item</li> </ul>
The next most useful class is list-inline, which will line up each <li> in a horizontal line.
Need to add a class of list-inline-item to each <li> tag.

‌DESCRIPTION LIST

‌Align terms and descriptions horizontally by using our grid system’s predefined classes like row and col
For longer terms, add a .text-truncate class to truncate the text with an ellipsis.
<dt class="col-sm-3 text-truncate">Truncated term is truncated</dt>
<dl class="row"> <dt class="col-sm-3">Description lists</dt> <dd class="col-sm-9">A description list is perfect for defining terms.</dd>

Bootstrap Images

2024-04-02T22:57:00.001+05:30

BOOTSTRAP IMAGES

Bootstrap allows you to do a few useful things with images using CSS classes. These things include: making images responsive, converting images to shapes, and aligning images.

MAKING IMAGES RESPONSIVE

Images in Bootstrap are made responsive with the .img-fluid class.

This applies max-width: 100%; and height: auto; to the image so that it scales with the parent width.

Can use .img-thumbnail to give an image a rounded 1px border appearance.

USING IMAGE SHAPES

Bootstrap 4 uses three different shape styles that can be applied to images:

· img-rounded will add round corners to your image

· img-circle will crop your image into a circle

· img-thumbnail will add round corners and a border to make the image look like a thumbnail

Bootstrap 5 replaced the above classes with the classes given below.

<img src="..." class="rounded" alt="..."><

img src="..." class="rounded-top" alt="...">

Rounded corner sizes range from 0 to 5

ALIGNING IMAGES

Align images with the helper float classes or text alignment classes.

Block-level images can be centered using the .mx-auto margin utility class.

</div>

Bootstrap Tables

2024-04-02T14:59:00.000+05:30

BOOTSTRAP TABLES

The basic table structure in Bootstrap takes advantage of almost all the available HTML table tags. Add the base class .table to any <table

All table styles are not inherited in Bootstrap, meaning any nested tables can be styled independently from the parent.

TABLE CLASS VARIANTS

Use contextual classes to colour tables, table rows or individual cells.

‌

Table Classes

Class-Name	Description	Example
table-striped	to add zebra-striping to any table row within the `<tbody>`	<table class="table table-striped">
table-striped-columns	to add zebra-striping to any table column.	<table class="table table-striped-columns">
.table-hover	to enable a hover state on table rows within a `<tbody>`.	<table class="table table-hover">
table-active	To highlight a table row or cell by adding this class.	<table class="table"> <thead> ... </thead> <tbody> <tr class="table-active">
table-bordered	To add borders on all sides of the table and cells.	<table class="table table-bordered">
table-borderless	To prepare a table without borders.	<table class="table table-borderless"> ...
table-sm	to make any `table` more compact by cutting all cell `padding` in half.	<table class="table table-sm">
table-hover	adds a hover effect (grey background color) on table rows:	<table class="table table-hover">
table-dark	adds a black background to the table	<table class="table table-dark">
table-dark and .table-striped	to create a dark, striped table	<table class="table table-dark table-striped">
table-responsive	adds a scrollbar to the table when needed	<div class="table-responsive"> <table class="table"> ... </table> </div>

RESPONSIVE TABLES

Possible to decide when the table should get a scrollbar, depending on the screen width:

Class	Screen width
.table-responsive-sm	< 576px
.table-responsive-md	< 768px
.table-responsive-lg	< 992px
.table-responsive-xl	< 1200px
.table-responsive-xxl	< 1400px

SAMPLE SCRIPT

<!doctype html>

<html>

<head>

<title>Navigation Bootstrap</title>

</head>

<body>

<thead>

<th>First</th>

<th>Handle</th>

</tr>

</thead>

<tbody>

<tr>

</tr>

<tr>

<td>Jacob</td>

<td>Thornton</td>

</tr>

<tr>

<td colspan="2">Larry the Bird</td>

<td>@twitter</td>

</tr>

</tbody>

</table>

</body>

</html>

UNIT - I Notes

2024-02-07T22:36:00.000+05:30

Operation Research - Definition

Operations research is essentially a collection of mathematical techniques and tools which in conjunction with a system’s approach, are applied to solve practical decision problems of an economic or engineering nature.

General Structure of an LP Model

The general structure of an LP model consists of the following three basic components (or parts).

· Decision variables (activities)

· The objective function

· The constraints

Decision Variables

To arrive at the optimal value of the objective function, certain activities (also called decision variables) usually denoted by x1, x2, . . ., xn are conducted. In an LP model, all decision variables are continuous, controllable and non-negative. That is, x1 ≥ 0, x2 ≥ 0, . . ., xn ≥ 0.

Objective Function

The objective function of each LP problem is expressed in terms of decision variables to optimize the criterion of optimality (also called measure-of-performance) such as profit, cost, revenue, distance etc.

In its general form, it is represented as:

Optimize (Maximize or Minimize) Z = c₁x₁ + c₂x₂ + . . . + c_nx_n

The Constraints

There are always certain limitations (or constraints) on the use of resources, such as: labour, machine, raw material, space, money, etc. Such constraints must be expressed as linear equalities or inequalities in terms of decision variables. The solution of an LP model must satisfy these constraints.

IMPORTANT DEFINITIONS

Solution

The set of values of decision variables xj (j = 1, 2, . . ., n) that satisfy the constraints of an LP problem is said to constitute the solution to that LP problem.

Feasible solution

The set of values of decision variables xj (j = 1, 2, . . ., n) that satisfy all the constraints and non-negativity conditions of an LP problem simultaneously is said to be the feasible solution of the LPP.

Infeasible solution

The set of values of decision variables xj ( j = 1, 2, . . ., n) that do not satisfy all the constraints and non-negativity conditions of an LP problem simultaneously is said to be the infeasible solution of the LPP.

Basic solution

For a set of m simultaneous equations in n variables (n > m) in an LP problem, a solution obtained by setting (n – m) variables equal to zero and solving for remaining m equations in m variables is called a basic solution of that LP problem.

The (n – m) variables whose value did not appear in the basic solution are called non-basic variables and the remaining m variables are called basic variables.

Basic feasible solution

A feasible solution to an LP problem which is also the basic solution is called the basic feasible solution. That is, all basic variables assume non-negative values.

The basic feasible solution is of two types:

(a) Degenerate A basic feasible solution is called degenerate if the value of at least one basic variable is zero.

(b) Non-degenerate A basic feasible solution is called non-degenerate if the value of all m basic

variables are non-zero and positive.

Optimum basic feasible solution

A basic feasible solution that optimizes (maximizes or minimizes) the objective function value of the given LP problem is called an optimum basic feasible solution.

Unbounded solution

A solution that can increase or decrease infinitely the value of the objective function of the LP problem is called an unbounded solution.

Deﬁnition of Linear Programming

Linear programming is a mathematical technique for determining the optimal allocation of resources among alternative uses of the resources to achieve a particular objective. The objective includes proﬁt maximization or cost minimization.

Optimal condition

For maximization problems if all Cj - Zj are less than equal to 0, then the optimal condition is reached otherwise select the variable with the maximum Cj - Zj as the entering variable.

For minimization problems if all Cj - Zj are greater than equal to 0, then the optimal condition is reached; otherwise, select the variable with the most negative value as the entering variable.

The canonical form of LPP

The given LPP can be written in a canonical form as follows;

1) The objective function is of maximization type. If the given objective function is of minimization type, convert it into maximization type by multiplying throughout by -1.

2) All the constraints are of ≤ type. The inequalities of ≥ type are converted to ≤ type by multiplying both sides of the inequality by -1.

3) All the variables are non-negative.

If a variable is unrestricted in sign, replace it with the difference between two positive variables. For example, if x_i is unrestricted in sign, replace it with x_i' - x_i''

Standard form of LPP

1) All constrains / inequalities are written as equations.

To convert a ≤ inequality to an equation add a variable to the left-hand side of the constraint. This variable is called a slack variable.

To convert a ≥ inequality to an equation subtract a variable from the left-hand side of the constraint. This variable is called a surplus variable.

2) The right-hand side of the inequalities must be non-negative.

If the right-hand side is negative, then multiply both sides of the constraint by -1 in which case the ≤ inequality will be changed to ≥ and vice-versa.

Simplex Method

Step 1: Rewrite the given LPP in the standard form.

a) Check whether the objective function is of maximization type.

b) Check whether all the right-hand side values of the constraints are non-negative.

c) Convert all the inequalities into equations.

Step 2: Obtain an initial basic feasible solution and put it under the Basic Variable(BV) column of the initial Simplex table.

Step 3: Compute the net evaluations zj = ∑(C_Bi - y_ij). Then calculate C_j-Z_j

Step 4: Check for optimal conditions. If at least one (C_j-Z_j) is negative, then choose the most negative of them and the corresponding column variable is taken as the entering column variable.

Step 5 : To ﬁnd the leaving variable, ﬁnd the ratio of bi / x_i (xi positive values in the entering column).

Step 6: The minimum ratio is taken as the leaving variable. This variable in the BV column will be replaced with the entering column variable.

Step 7 : The element at the intersection of the Key column and key row is called the pivot element.

Step 8: Construct the next simplex table in such a way that the pivot element must be 1 and the other elements in the key column must be 0.

Step 9 : Repeat steps 3 to 8, till the optimal condition is obtained.

Artiﬁcial Variable

While converting ≥ inequality to an equation, a variable called surplus variable is subtracted from the left-hand side of the equation. The addition of this variable will not satisfy the feasibility condition. Hence, to ﬁnd the optimal solution using the Simplex method, a variable called an Artiﬁcial Variable is added to the left-hand side of the equation.

While using the Simplex method to ﬁnd the optimal solution to the LPP, the artiﬁcial variables must be removed.

There are two methods for removing artiﬁcial variables from the solution.

• Two-Phase Method

• Big-M Method or Method of Penalties

Two Phase Simplex Method

Phase I

Step 1 (a):

If the constraints in the given LP problem are (≥) type, then the necessary number of surplus and artiﬁcial variables are added to convert constraints into equality constraints.

(b) If the given LP problem is of minimization, then convert it to maximization

Step 2: Assign zero coeﬃcient to each of the decision variables (xj ) and the slack

and surplus variables; and assign – 1 coeﬃcient to each of the artiﬁcial variables. This yields the following auxiliary LP problem.

Step 3: Apply the simplex algorithm to solve this auxiliary LP problem.

The following three cases may arise at optimality.

(a) Max Z * = 0 and at least one artiﬁcial variable is present in the basis with a positive value. This means that no feasible solution exists for the original LP problem.

(b) Max Z * = 0 and no artiﬁcial variable is present in the basis. This means that only decision variables (xj ’s) are present in the basis and hence proceed to Phase II to obtain an optimal basic feasible solution on the original LP problem.

(c) Max Z * = 0 and at least one artiﬁcial variable is present in the basis at zero value. This means that a feasible solution exists and proceed directly to Phase II or else eliminate the artiﬁcial basic variable and then proceed to Phase II.

Phase II:

Assign actual coeﬃcients to the variables in the objective function and zero coeﬃcient to the artiﬁcial variables which appear at zero value in the basis at the end of Phase I.

The last simplex table of Phase I can be used as the initial simplex table for Phase II.

Then apply the usual simplex algorithm to the modiﬁed simplex table to get the optimal solution to the original problem.

Artiﬁcial variables that do not appear in the basis column can be removed from the table.

Big-M Method

Big-M method is another method of removing artiﬁcial variables from the basis.

In this method, a large penalty (M) is added as coeﬃcient to artiﬁcial variables in the objective function. The penalty is supposed to be designated by – M, for a maximization problem, and + M, for a minimization problem, where M > 0.

The Big-M method for solving an LP problem can be summarized in the following steps:

Step 1:

Express the LP problem in the standard form by adding slack variables, surplus variables and artiﬁcial variables.

Assign a zero coeﬃcient to both slack and surplus variables.

Then assign a very large coeﬃcient + M (minimization case) and – M (maximization case) to artiﬁcial variable in the objective function.

Step 2:

The initial basic feasible solution is obtained by assigning zero value to decision variables, x1, x2, ..., etc.

Step 3:

Calculate the values of cj – zj in last row of the simplex table and examine these values.

(i) If all cj – zj ≥ 0, then the current basic feasible solution is optimal.

(ii) If for a column, k, c_k – z_k is most negative and all entries in this column are negative, then the problem has an unbounded optimal solution.

(iii) If one or more cj – zj < 0 (minimization case), then select the variable with the largest negative cj – zj value (largest value) as the entering variable.

Step 4: Determine the key row and key element in the same manner as done in the simplex algorithm for the maximization case.

Step 5: Continue with the procedure to update solution at each iteration till the optimal solution is obtained.

String Handling in Java

2023-10-12T21:14:00.003+05:30

String Handling

Java implements strings as objects of type String.

Java provides a full complement of features that make string handling convenient. For example, Java has methods to compare two strings, search for a substring, concatenate two strings, and change the case of letters within a string.

Strings are immutable. That is, once a String object has been created, the characters that comprise that string cannot be changed. The original string is left unchanged.

To create mutable strings (ie strings whose content can be changed), Java provides two options: StringBuffer and StringBuilder. Both hold strings that can be modified after they are created.

String objects can be constructed in several ways, making it easy to obtain a string when needed.

String Constructors

String s = new String(); //default

char ch[] = { 'a', 'b', 'c' };

String s = new String(ch); //converting array of characters to string

char ch[] = { 'a', 'b', 'c', 'd', 'e', 'f' };

String s = new String(ch, 2, 3); //s="cde" from second position to 3 characters

String(String strObj) //copy constructor

char c[] = {'J', 'a', 'v', 'a'};

String s1 = new String(c);

String s2 = new String(s1);

byte ascii[] = {65, 66, 67, 68, 69, 70 };

String s1 = new String(ascii); //s1=ABCDEF

byte ascii[] = {65, 66, 67, 68, 69, 70 };

String s1 = new String(ascii,3,2); //s1=DE

String(StringBuffer strBufObj) //StringBuffer is a pre-defined class in Java

// Construct one String from another.

class MakeString

{

public static void main(String args[])

{

char c[] = {'J', 'a', 'v', 'a'};

String s1 = new String(c);

String s2 = new String(s1);

System.out.println(s1);

System.out.println(s2);

}

String Concatenation

In general, Java does not allow operators to be applied to String objects. The one exception to this rule is the + operator, which concatenates two strings, producing a String object as the result. This allows you to chain together a series of + operations. For example, the following fragment concatenates three strings:

String age = 10;

String s = “He is “ + age + ” years old”;

Java String class methods

The java.lang.String class provides many useful methods to perform operations on a sequence of char values.

Character Extraction

The String class provides several ways in which characters can be extracted from a String object. Some of the methods defined in the String class for this purpose are:

· charAt()
· getChars()
· getBytes()
· toCharArray()

charAt()

The charAt() method returns a char value at the given index number.

The index number starts from 0 and goes to n-1, where n is the length of the string. It returns StringIndexOutOfBoundsException if the given index number is greater than or equal to this string length or a negative number.

public class CharAtExample{

public static void main(String args[]){

String name="Strings in Java";

char ch=name.charAt(4); //returns the char value at the 4th index

System.out.println(ch);

}}

getChars()

To extract more than one character at a time, use the getChars() method. It has this general form:

void getChars(int sourceStart, int sourceEnd, char target[ ], int targetStart)

Example

String s = "This is a demo of the getChars method.";

int start = 10;

int end = 14;

char buf[] = new char[end - start];

s.getChars(start, end, buf, 0);

System.out.println(buf); //will store demo in buf

getBytes()

There is an alternative to getChars( ) that stores the characters in an array of bytes. This method uses the default character-to-byte conversions provided by the platform. Here is its simplest form:

byte[ ] getBytes( )

toCharArray( )

To convert all the characters in a String object into a character array, the easiest way is to call toCharArray( ). It returns an array of characters for the entire string. It has this general form:

char[ ] toCharArray( )

Java String length()

The java string length() method length of the string. It returns the count of total number of characters. The length of the Java string is the same as the Unicode code units of the string.

public class LengthExample{

public static void main(String args[]){

String s1="java";

String s2="python";

System.out.println("string length is: "+s1.length()); //4 is the length of javatpoint string

System.out.println("string length is: "+s2.length()); //6 is the length of python string

}}

Java String substring()

The java string substring() method returns a part of the string.

We pass the begin index and end index number position in the Java substring method where the start index is inclusive and the end index is exclusive. In other words, the start index starts from 0 whereas the end index starts from 1.

There are two types of substring methods in Java string.

1. public String substring(int startIndex)

2. public String substring(int startIndex, int endIndex)

Example

public class SubstringExample{

public static void main(String args[]){

String s1="java Program";

System.out.println(s1.substring(2,4));//returns va

System.out.println(s1.substring(2));//returns va Program

}}

Java String equals()

The java string equals() method compares the two given strings based on the content of the string. If any character is not matched, it returns false. If all characters are matched, it returns true.

The String equals() method overrides the equals() method of the Object class.

public class EqualsExample{

public static void main(String args[]){

String s1="hello";

String s2="hello";

String s3="HELLO";

String s4="python";

System.out.println(s1.equals(s2));//true because content and case is same

System.out.println(s1.equals(s3));//false because case is not same

System.out.println(s1.equals(s4));//false because content is not same

System.out.println(s1.compareTo(s4));

}}

Java String compareTo

The String compareTo() method compares values lexicographically and returns an integer value that describes if the first string is less than, equal to, or greater than the second string.

Suppose s1 and s2 are two string variables. If:

s1 == s2 : 0

s1 > s2 : positive value (difference of character value)

s1 < s2 : negative value

Example

public static void main(String args[])

{

String s1="hello";

String s2="hello";

String s3="meklo";

String s4="hemlo";

String s5="flag";

System.out.println(s1.compareTo(s2)); //0 because both are equal

System.out.println(s1.compareTo(s3));//because "h" is 5 times lower than "m"

System.out.println(s1.compareTo(s4));//1 because "l" is 1 times lower than "m"

System.out.println(s1.compareTo(s5)); //2 because "h" is 2 times greater than "f"

}

Java String concat

The java string concat() method combines the specified string at the end of this string. It returns a combined string. It is like appending another string.

public class ConcatExample{

public static void main(String args[]){

String s1="java string";

s1.concat("is immutable");

System.out.println(s1);

s1=s1.concat(" is immutable so assign it explicitly");

System.out.println(s1);

}}

Java String isEmpty()

The java string isEmpty() method checks if this string is empty or not. It returns true if the length of the string is 0 otherwise false. In other words, true is returned if the string is empty otherwise it returns false.

The isEmpty() method of the String class has been included in the Java string since JDK 1.6.

public class IsEmptyExample{

public static void main(String args[]){

String s1="";

String s2="java";

System.out.println(s1.isEmpty());

System.out.println(s2.isEmpty());

}}

Daily Coding Problem (18-8-2023)

2023-08-18T23:53:00.001+05:30

Good morning! Here's your coding interview problem for today.

This problem was asked by Google.

You are given an array of nonnegative integers. Let's say you start at the beginning of the array and are trying to advance to the end. You can advance at most, the number of steps that you're currently on. Determine whether you can get to the end of the array.

For example, given the array [1, 3, 1, 2, 0, 1], we can go from indices 0 -> 1 -> 3 -> 5, so return true.

Given the array [1, 2, 1, 0, 0], we can't reach the end, so return false.

You can write the program in any programming language.

Operation Research MCQ

2023-08-07T13:04:00.002+05:30

1. What type of approach does operation research have?

a) multi-disciplinary b) scientific c) intuitive d) all of the above

2. OR approach is typically based on the use of

a) Physical model b) Mathematical model c) Iconic model d) Descriptive model

3. Which of the following is not a characteristic of the LP model?

a) alternative courses of action
b) an objective function of maximization type
c) limited number of resources
d) non-negativity condition on the value of decision variables

4. What is the objective function in linear programming problems?

a) A constraint for available resource
b) An objective for research and development of a company
c) A linear function in an optimization problem
d) A set of non-negativity conditions

5. Which statement characterizes standard form of a linear programming problem?

a) Constraints are inequalities of any type b) Constraints are a set of linear equations

c) Constraints are inequalities of >= type d) Constraints are inequalities of <= type

6. In graphical representation, what is the name of the bounded region?

a) solution b) basic solution c) feasible solution d) optimal solution

7. If two constraints do not intersect in the positive quadrant of the graph, then ____________.

a) the problem is infeasible b) the solution is unbounded

c) one of the constraints is redundant d) none of the above

8. What type of LPP can be solved using graphical method?

a) LPP with two decision variables b) LPP with three decision variables

c) LPP with one decision variable d) LPP with any number of decision variables

9. How many columns will there be in the Simplex table, if there are ‘M’ original variables and ‘n’ introduced variables?

a) M + n b) M - n c) M + n + 1 d) M + n - 1

10. Name the variable that is added to the constraints of type ‘=’.

a) surplus variable b) dummy variable c) slack variable d) artificial variable

11. If all aij values in the entering variable column of the simplex table are negative, then ______________.

a) solution is unbounded b) solution is degenerate

c) there exists no solution d) there are multiple solutions

12. A BFS of an LPP is said to be ________, if at least one of the basic variables is zero.

a) Infeasible b) non-degenerate c) Feasible d) Degenerate

13. A minimization problem can be converted into a maximization problem by changing the sign of coefficients in the ‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐

a) objective function only b) constraints only

c) both objective function and constraints d) basis variables only

14. All the constraints are expressed as equations and the right-hand side of each constraint, and all variables are non-negative is called _______

a) Standard form of LPP b) Simplex form of LPP

c) Canonical form of LPP d) General form of LPP

15. If dual has an unbounded solution, primal has _________.

a) no feasible solution b) unbounded solution c) feasible solution d) an optimal solution

16. If a primal LP problem has a finite solution, then the dual LP problem should have __________.

a) finite solution b) infeasible solution c) unbounded solution d) feasible solution

17. The dual of the dual is ______________.

a) dual-primal b) primal-dual c) primal d) dual

18. How are the dual constraints for the maximization LP problem written?

a) Σ aij yi ≥ cj b) Σ aji yi ≥ cj c) Σ aij yi ≤ cj d) Σ aji yi ≤ cj

19. The right-hand side constant of a constraint in a primal problem appears in the corresponding dual as __________.

a) a coefficient in the objective function b) a right-hand side constant of a constraint

c) an input-out coefficient d) none of the above

20. Variable in dual problem which can assume negative values, positive values or zero value is classified as _________________.

a) slack variable b) restricted variable c) unrestricted variable d) decision variable

21. The dummy source or destination in a transportation problem is added to _____________

a) satisfy rim conditions b) prevent solution from becoming degenerate

c) ensure that total cost does not exceed a limit d) the solution not be degenerate

22. Which of the following methods is used to verify the optimality of the current solution of the transportation problem?

a) Least cost method b) Vogel’s approximation method

c) North-west corner method d) Modified Distribution Method

23. If demand is lesser than supply then dummy demand node is added to make it a __________

a) Simple problem b) Balanced problem

c) Transportation problem d) Assignment problem

24. One disadvantage of using North-West Corner rule to find initial solution to the transportation problem is that ___________.

a) It is complicated to use b) It does not consider cost of transportation

c) It leads to a degenerate initial solution d) It does not lead to optimal solution

25. In an assignment problem involving 5 workers and 5 jobs, total number of assignments possible are ______________

a) 10 b) 25 c) 5 d) 1

26. In assignment problem of maximization, the objective is to maximize the _______.

a) cost b) time c) profit d) loss

27. Both transportation and assignment problems are members of a category of LP problems called ______

a) shipping problems b) network flow problem

c) logistic problems d) routing problems

28. In sensitivity analysis of the coefficient of the non-basic variable in a cost minimization LP problem, the upper sensitivity limit is ________________.

a) original value + Lowest positive value of improvement ratio
b) original value – Lowest absolute value of improvement ratio
c) positive infinity
d) negative infinity

29. The entering variable in the sensitivity analysis of objective function coefficients is always a ____.

a) decision variable b) non-basic variable c) basic variable d) slack variable

30. A change in the objective function for a non-basic variable can affect _____________.

a) cj – zj values of all non-basic variables b) cj – zj values of all basic variables

c) Only the cj – zj value of that variable d) the initial basic feasible solution

ANSWER

1.a	2. b	3. b	4. c	5. a	6. c	7. a	8. a	9. a	10. d
11. a	12. d	13. a	14. c	15. a	16. a	17. c	18. b	19. a	20. c
21. a	22. d	23. b	24. b	25. c	26. c	27. b	28. c	29. d	30. c

Google App Engine

2023-05-05T23:24:00.001+05:30

Google AppEngine

Google AppEngine is a PaaS implementation
AppEngine is essentially a distributed and scalable runtime environment
Developers can develop applications in Java, Python, and Go
Go - a new programming language developed by Google to simplify the development of Web applications.

Architecture and core concepts

The platform is logically divided into four major components:

infrastructure,
the runtime environment,
the underlying storage,
the set of scalable services

1 Infrastructure

AppEngine hosts Web applications, and its primary function is to serve users requests efficiently.
The infrastructure is also responsible for monitoring application performance and collecting statistics on which the billing is calculated.

2 Runtime environment

It represents the execution context of applications hosted on AppEngine.
Sandboxing

One of the major responsibilities of the runtime environment is to provide the application environment with an isolated and protected context in which it can execute without causing a threat to the server

Users can develop AppEngine applications using three different languages and related technologies: Java, Python, and Go.

3 Storage

There are three different levels of storage:

in memory-cache,
storage for semi-structured data,
long-term storage for static data.

Static file servers

Web applications are composed of dynamic and static data.

Static data files can be hosted on static file servers, since they are not frequently modified.

DataStore

DataStore is a service that allows developers to store semi-structured data.

DataStore provides high-level abstractions that simplify interaction with Bigtable

DataStore also provides facilities for creating indexes on data and to update data

DataStore has been designed to be extremely fast in returning result sets

AppEngine uses an optimistic concurrency control: If one user tries to update an entity that is already being updated, the control returns and the operation fails.

4 Application services

These services simplify most of the common operations that are performed in Web applications:

access to data,
account management,
integration of external resources,
messaging and communication,
image manipulation
asynchronous computation.

UrlFetch

capability of retrieving a remote resource through HTTP/HTTPS by means of the UrlFetch service.

MemCache

AppEngine provides caching services by means of MemCache.

This is a distributed in-memory cache that is optimized for fast access.

Mail and instant messaging

Communication is another important aspect of Web applications.
AppEngine provides also another way to communicate with the external world: the Extensible Messaging and Presence Protocol (XMPP).
Any chat service that supports XMPP, such as Google Talk, can send and receive chat messages to and from the Web application,

Account management

AppEngine simplifies account management by means of Google Accounts.

The use of Google Accounts requires users to have a Google account,

The use of Google Accounts is particularly advantageous for developing Web applications within a corporate environment using Google Apps.

Image manipulation

Web applications render pages with graphics.

AppEngine allows applications to perform image resizing, rotation, mirroring, and enhancement by means of Image Manipulation

5 Compute services

Users navigate the Web pages and get instantaneous feedback in response to their actions.
This feedback is often the result of some computation happening on the Web application.
AppEngine offers additional services such as Task Queues and Cron Jobs.

Task queues

Task Queues allow applications to submit a task for a later execution. This service is particularly useful for long computations that cannot be completed within the maximum response time of a request handler.

Cron jobs

Sometimes a required operation needs to be performed at a specific time of the day,

It is possible to schedule the required operation at the desired time by using the Cron Jobs service.

Application life cycle

The life cycle of an application:

testing and development,

deployment,

monitoring

The SDKs released by Google provide developers with most of the functionalities required by these tasks.

Currently there are two SDKs available for development: Java SDK and Python SDK.

1 Application development and testing

Developers can start building their Web applications on a local development server.
The development server simulates the AppEngine runtime environment
The development server contains a complete set of monitoring features that are helpful to profile the behavior of applications.
The development server analyzes application behavior while running and traces all the queries made during testing and development.

Java SDK

Using the Eclipse software installer, it is possible to download and install Java SDK, Google Web Toolkit, and Google AppEngine plug-ins into Eclipse.

These three components allow developers to program powerful and rich Java applications for AppEngine

Developers can easily create Web applications by using the Eclipse Web Platform, which provides a set of tools and components.

The plug-in allows developing, testing, and deploying applications on AppEngine.

Python SDK

The Python SDK allows developing Web applications for AppEngine with Python 2.5.

It provides a standalone tool, called GoogleAppEngineLauncher

The Python implementation of the SDK also comes with an integrated Web application framework called webapp.

Webapp includes a set of models, components, and tools that simplify the development of Web applications.

Another Web framework that is known to work well is Django.

2 Application deployment and management

Once the application has been developed and tested, it can be deployed on AppEngine with a simple click or command-line tool.
Developers use an app identifier to upload and update applications.
Once an application identifier has been created, it is possible to deploy an application on AppEngine.
Once the application is uploaded, nothing else needs to be done to make it available.
AppEngine will take care of everything. Developers can then manage the application by using the administrative console.

3 Cost model

AppEngine provides a free service with limited quotas that get reset every 24 hours.

Once the application has been tested and tuned for AppEngine, it is possible to set up a billing account and obtain more allowance and be charged on a pay-per-use basis.

An application is measured against billable quotas, fixed quotas, and per-minute quotas.

Google AppEngine uses these quotas to ensure that users do not spend more than the allocated budget

Cloud platforms

2023-05-05T11:14:00.000+05:30

Cloud Platforms in Industry

An overview of a few prominent cloud computing platforms and a brief description of the types of service they offer are shown in the following table.

1 Amazon web services

The services offered by AWS are classified into 4 categories.

1. Compute services

2. Storage services

3. Communication services

4. Additional services

Amazon compute services

Most important compute services are

1. EC2 (Elastic Cloud Computing)

2. AMI (Amazon Machine Instances/Images)

Additional compute services are

1. Amazon Elastic Beanstalk

2. Amazon cloudFormation

3. Amazon MapReduce

The following figure shows the list of services offered under each category.

1.1 Compute services

The fundamental service in this space is Amazon EC2,
Amazon EC2 allows deploying servers in the form of virtual machines.
Each virtual machine is created as instances of a specific image.
Images come with a preinstalled operating system and a software stack.
The instances can be configured for memory, number of processors, and storage.

1.1.1 Amazon machine images

(AMIs) are templates from which it is possible to create a virtual machine.
They are stored in Amazon S3 and identified by a unique identifier in the form of ami-xxxxxx.
An AMI contains a physical file system layout with a predefined operating system installed.
AMIs are either created from scratch or “bundled” from existing EC2 instances.
Once an AMI is created, it is stored in an S3 bucket and the user can decide whether to make it available to other users or keep it for personal use.

1.1.2 EC2 instances

EC2 instances represent virtual machines. They are created using AMI as templates.

There are six major categories of EC2 instances available as given below:

Standard instances. This class offers a set of configurations that are suitable for most applications.
Micro instances. This class is suitable for those applications that consume a limited amount of computing power and memory. Micro instances can be used for small Web applications with limited traffic..
High-memory instances. This class targets applications that need to process huge workloads and require large amounts of memory.
High-CPU instances. This class targets compute-intensive applications.
Cluster Compute instances. This class is used to provide virtual cluster services. Instances in this category are characterized by high CPU compute power and large memory.
Cluster GPU instances. This class provides instances featuring graphic processing units (GPUs) and high compute power, large memory, and extremely high I/O and network performance.

1.1.3 EC2 environment

EC2 instances are executed within a virtual environment
By default, instances are created with an internal IP address.
Together with an external IP, EC2 instances are also given a domain name.
Instance owners can partially control where to deploy instances.
Amazon EC2 controls the accessibility of a virtual instance with basic firewall configuration.

1.1.4 Advanced compute services

Amazon Web Services provide more sophisticated services in addition to EC2 and AMI.

AWS CloudFormation

CloudFormation introduces the concepts of templates, which are JSON formatted text files.
CloudFormation allows easy and explicit linking EC2 instances together and introducing dependencies among them.
Templates provide a simple and declarative way to build complex systems
Allows to integrate EC2 instances with other AWS services such as S3, SimpleDB, SQS, SNS, Route 53, Elastic Beanstalk, and others.

AWS elastic beanstalk

AWS Elastic Beanstalk constitutes a simple and easy way to package applications and deploy them on the AWS Cloud.
This service is available only for Web applications developed with the Java/Tomcat technology stack.
Developers can conveniently package their Web application into a WAR file and use Beanstalk to automate its deployment on the AWS Cloud.

Amazon elastic MapReduce

It utilizes Hadoop as the MapReduce engine,
deployed on a virtual infrastructure composed of EC2 instances,
and uses Amazon S3 for storage needs.
MapReduce introduces elasticity and allows users to dynamically size the Hadoop cluster
EC2 instances to compose the cluster (Small, High-Memory, High-CPU, Cluster Compute, and Cluster GPU).

1.2. Amazon storage services

The core storage service by Amazon is Simple Storage Service (S3).
This is a distributed object store that allows users to store information in different formats.
The core components of S3 are two:

buckets - Buckets represent virtual containers in which to store objects
objects - objects represent the content that is actually stored. Can also store metadata about the stored content.

1.2.1 S3 key concepts

The storage is organized in a two-level hierarchy.
Stored objects cannot be manipulated like standard files

Once an object has been added to a bucket, its content and position is immutable

Content is not immediately available to users.
Requests will occasionally fail.

Due to the large distributed infrastructure being managed, requests for object may occasionally fail.

Resource Naming

Amazon offers three different ways of addressing a bucket

Canonical form: http://s3.amazonaws.com/bukect_name/object_name
Subdomain form: http://bucket-name/s3.amzonaws.com/object_name
Virtual hosting form: http://bucket-name.com/object_name

Subdomain form: http://bucketname.s3.amazon.com/.

To express a bucket name in this form, the name has to do all of the following:

Be between 3 and 63 characters long
Contain only letters, numbers, periods, and dashes
Start with a letter or a number.
Contain at least one letter
Have no fragments between periods that start with a dash or end with a dash or that are empty strings

This form is equivalent to the previous one when it can be used, but it is the one to be preferred since it works more effectively for all the geographical locations serving resources stored in S3.

Access control and security

Amazon S3 allows controlling the access to buckets and objects by means of Access Control Policies (ACPs).

An ACP is a set of grant permissions that are attached to a resource.

Currently, five different permissions can be used:

READ allows the grantee to retrieve an object and its metadata and to list the content of a bucket as well as getting its metadata.

WRITE allows the grantee to add an object to a bucket as well as modify and remove it.

READ_ACP allows the grantee to read the ACP of a resource.

WRITE_ACP allows the grantee to modify the ACP of a resource.

FULL_CONTROL grants all of the preceding permissions.

Other storage services

Amazon elastic block store

The Amazon Elastic Block Store (EBS) allows AWS users to provide EC2 instances with persistent storage in the form of volumes that can be mounted at instance startup.

Amazon ElastiCache

ElastiCache is an implementation of an elastic in-memory cache based on a cluster of EC2 instances. It provides fast data access from other EC2 instances.

Structured storage solutions

Amazon provides structured storage services in three different forms:

preconfigured EC2 AMIs
Amazon Relational Data Storage (RDS)
Amazon SimpleDB.

Amazon RDS

Two key advanced features of RDS are multi-AZ deployment and read replicas.

The first option provides users with a failover infrastructure for their RDBMS solutions.
The second option provides users with increased performance for applications that are heavily based on database reads.

Amazon SimpleDB

Amazon SimpleDB is a lightweight, highly scalable, and flexible data storage solution for applications.

SimpleDB provides support for semi-structured data,

The model is based on the concept of domains, items, and attributes.

Provides improved performance in querying large quantities of data.

Amazon CloudFront

CloudFront is an implementation of a content delivery network on top of the Amazon distributed storage infrastructure.
The content that can be delivered through CloudFront is static (HTTP and HTTPS) or streaming.
CloudFront is cheaper than S3.
CloudFront is designed to optimize the distribution of very popular content that is frequently downloaded.

1.3 Communication services

Amazon provides facilities to structure and facilitate the communication among existing applications.

These facilities can be organized into two major categories:

virtual networking
messaging.

1.3.1 Virtual networking

Virtual networking comprises a collection of services that allow AWS users to control the connectivity to and between compute and storage services.
Amazon Virtual Private Cloud (VPC) and Amazon Direct Connect provide connectivity solutions in terms of infrastructure;
Route 53 facilitates connectivity in terms of naming

Amazon VPC

It provides a great degree of flexibility in creating virtual private networks within the Amazon infrastructure.

Amazon Direct Connect

It allows AWS users to create dedicated networks between the user private network and Amazon Direct Connect locations, called ports.

Amazon Route 53

It implements dynamic DNS services that allow AWS resources to be reached through domain names.

1.3.2 Messaging

The three different types of messaging services offered are

Amazon Simple Queue Service (SQS),
Amazon Simple Notification Service (SNS),
Amazon Simple Email Service (SES).

Amazon SQS

constitutes disconnected model for exchanging messages between applications by means of message queues, hosted within the AWS infrastructure.

Amazon SNS

provides a publish-subscribe method for connecting heterogeneous applications.

Amazon SNS allows applications to be notified when new content of interest is available

Amazon SES

provides AWS users with a scalable email service that leverages the AWS infrastructure.

Once users are signed up for the service, they have to provide an email that SES will use to send emails on their behalf.

To activate the service, SES will send an email to verify the given address and provide the users with the necessary information for the activation.

Upon verification, the user is given an SES sandbox to test the service, and he can request access to the production version. Using SES, it is possible to send either SMTP-compliant emails or raw emails by specifying email headers and Multipurpose Internet Mail Extension (MIME) ty

Cloud Security and Privacy

2023-04-20T06:45:00.000+05:30

Cloud Security and Privacy

Chapter 17

17.1 Cloud-Specific Security Problems

Several factors contribute to the complexity of managing cloud computation

Lack of control and visibility
An infrastructure shared with outsiders
Many services with interdependencies among them.
Dynamic execution environment with bursts
Remote access for all users
Extensive use of software from the cloud providers and third parties

Lack of control and visibility.

In a cloud environment, a tenant cannot configure or examine the underlying systems

Must trust that the provider’s staff has configured security protections correctly.

An infrastructure shared with outsiders

running multiple tenants on the same infrastructure increases security risks, and security and privacy breaches have occurred.

Many services with interdependencies among them.

having many microservices and allowing frequent communication among them increases the attack surface,

Dynamic execution environment with bursts.

Rapid creation of new instances makes it more difficult to distinguish normal execution from a Denial of Service (DoS) attack

Remote access for all users.

the use of remote access increases the possible attack surface

Extensive use of software from the cloud provider and third parties.

Building cloud-native software has added complexity, such as designing microservices that can be orchestrated.

17.2 The Zero Trust Security Model

How can a tenant know which individuals should be allowed to access and manage services?

The answer lies in a zero trust security model.

The idea is straightforward: assign each user a set of privileges for each possible service. Instead of merely allowing a user to login once and then have access to all services, validate each request separately. That is, whenever a user attempts to access a service, use the identity of the user (and possibly the identity of the user’s device) to decide whether to grant or deny the request.

17.3 Identity Management

To avoid having separate authentication for each service, an identity management system uses a Single Sign On (SSO), which means a user has the same login and password credentials for all services.

An Identity Management system

stores information about users’ identities and their access rights,
uses a single login for all services,
authenticates users,
ensures only authorized users access each service,
and allows a user to enter credentials once for each task.

17.4 Privileged Access Management (PAM)

A Privileged Access Management (PAM) system handles identity management for privileged accounts (administrative or superuser level of privilege).
PAM systems log all accesses, providing a detailed record of which individual accessed a system at a given time.
The systems also record failed login attempts, providing a way to track attackers.
If a staff member’s ID is used to access multiple secondary systems within a short time, the PAM system sends an alert to the manager reporting suspicious activity.

17.5 Protecting Remote Access

Three principles help define security practices:

Keep all communication confidential
Protect and isolate business data
Enforce workflow security

Keep all communication confidential

To keep communication confidential, all data must be encrypted.
Virtual Private Network (VPN), technology forms a connection to the organization’s cloud data center and encrypts all packets sent over the connection

Protect and isolate business data.

Remote access introduces an additional danger:an employee may lose a device that contains confidential business data.
To protect it from accidental loss, all business data stored on a user’s device must be encrypted.

Enforce workflow security.

As an employee performs a task, data may move from the cloud to the employee’s device and back.
To ensure that all data remains safe independent of its location, an organization must define a security policy for each workload.
Industry uses the term workflow security to characterize the approach.

17.6 Privacy In A Cloud Environment

Security systems enforce protections to guarantee the confidentiality, integrity, and availability of data.
Privacy refers to keeping sensitive information about an individual safe from public dissemination.
Privacy protection cannot focus only on the data at hand.
In addition, other aspects of security must be chosen to prevent violations of privacy.

17.7 Back Doors, Side Channels, And Other Concerns

Interestingly, privacy considerations intertwine with other aspects of data security.
An organization must be careful to avoid possible back doors and side channels that allow data to leak to unintended recipients.
Three points of contact between applications cause concern:

shared storage systems,
shared computing systems
shared networks

Instances have occurred where flaws, including flaws in the underlying hardware, allow data to transfer from one application to another through a side channel.
In addition, attackers try to insert back doors into systems that send copies of data to the attacker.
Tenants cannot predict or prevent flaws from occurring, but they can remain aware of the potential danger, and work hard to detect back doors.

A tenant must view a cloud service provider as a partner and work closely with the provider on security, both to ensure policies have been configured correctly and to handle problems that arise in the underlying infrastructure.

17.8 AI Technologies And Their Effect On Security

Interestingly, Artificial Intelligence (AI) technologies influence security in both positive and negative ways.

On the one hand, attackers can use AI techniques to bypass safeguards and gain unauthorized access to data or systems.
On the other hand, AI techniques can be used to strengthen safeguards.

Negative impact of AI

The approach is known as a deep fake.

An AI program that used machine learning (ML) was first fed recordings of the voice of a company executive so the program could learn the executive’s voice and speech patterns.

Once the learning phase was complete, the program imitated the voice while pronouncing text from a script.

The attacker left voice mail for an employee, apparently from the company executive, asking the employee to transfer confidential data to an external site.

Positive impact of AI

PAM systems can use AI software to detect various types of anomalous behavior of an employee under the general topic of security analytics.
If a machine learning program receives notification of each network connection that arrives from the Internet, the program may be able to detect an instance of a Distributed Denial of Service (DDoS) attack.
One final aspect of security analytics arises from context.

Suppose a given user always logs into the HR system and uses the system to update the employee database.
Security analytics software takes another view: it flags the access as unusual because it does not occur in the usual context.
Security analytics software can be context-aware.

Edge Computing and IIoT

2023-04-19T21:50:00.000+05:30

Chapter 16

Edge Computing and IIoT

16.1 Introduction

Although the cloud approach has many advantages, it does have the disadvantage of introducing higher network latency because a data center is remote from the customers it serves.

Note: Latency is the time it takes for data to pass from one point on a network to another.

Cloud providers attempt to minimize network latency in two ways:

The use of multiple, geographically diverse sites
Low-latency network connections

16.2 Situations Where Latency Matters

In the financial industry, for example, a small delay in making stock trades can result in a huge loss.
In the health care industry, a small delay in receiving data from a patient monitor can delay activation of an implanted medical treatment device.
Industries that employ real-time control systems — sensors and actuators that monitor and control processing — rely on low delay.

The following table lists some of the industries for which low latency can be important.

16.3 Moving Computing To The Edge

To meet the requirements for low latency in cloud computing, edge computing architecture is introduced.

Edge computing

Place some of the computing facilities near each source of information, and perform initial processing locally.
Computation performed near devices (smartphone) occurs near the edge instead of sending the data to a centralized cloud data center for processing.

Simultaneously run applications in a cloud data center, and use the cloud applications to handle computational-intensive tasks.

The following illustrates how edge computing works:

Lets assume the sensor monitors users heart ECG.

The data from the sensor is sent to the mobile phone to which the sensor is connected through an app.
The health care app running in the smartphone checks for any abnormality in the ECG signals.
If any abnormality is found, immediately a notification is sent to the doctor and the patients relatives for immediate action.

The edge computing approach places small, auxiliary data centers near locations that require low latency responses.

Software in the edge data center handles low-latency computations locally and runs other computations in a cloud data center.

16. 4 Extending Edge computing to Fog hierarchy

The locations and sizes of the edge data centers depend on the applications being supported and the latency requirements.
To achieve the lowest possible latency, an edge facility must be as close to each user as possible (e.g., in each cell tower).
For applications with less stringent requirements, an edge computing facility might serve a neighborhood of multiple cell towers or a geographic region with many neighborhoods.
To serve all applications, edge facilities can be organized into a hierarchy

Industry sometimes uses the term fog data center to refer to an intermediate data center that serves a larger geographic area.

16.5 Edge computing and IIoT

The term Industrial Internet of Things (IIoT) refers to an enhanced, larger-scale version of the Internet of Things.

The primary difference between consumer IoT systems and Industrial IoT systems lies in the importance: a company depends on an IIoT system as part of a critical business function.

Characteristics found in IIoT applications

Specific latency requirements
Geo-spatial knowledge
Large volumes of data with various QoS requirements
A need for data filtering
High availability requirements
Security requirements

Specific latency requirements.

IIoT applications have specific requirements (e.g., if a specific assembly line robot malfunctions, it must be shut down within 150 milliseconds after a problem is detected).

Geo-spatial knowledge.

An IIoT system must be aware of locations and spatial relationships.

Large volumes of data with various QoS requirements.

IIoT applications often employ many sensors and video cameras that each generate data continuously, resulting in large volumes of data;
Each type of data may have specific Quality of Service (QoS) requirements, such as data rates and bounds on latency.

A need for data filtering.

Applications running in the cloud only need data that allows them to analyze long-term trends. Hence it is not necessary to send all the raw data from sensors to the cloud.

High availability requirements

Since a company depends on IIoT systems to sustain their business, the systems must be reliable. Thus, IIoT may need to employ redundancy (duplication).

Security requirements.

IIoT systems must be secure from attack, and it must be possible to keep the data they gather confidential.

An IIoT system may transfer multiple types of data, each with its own requirements for performance, availability, and security.

16.6 Communications for IIoT

In an IIoT application data collected from sensors are transferred to different locations like cloud data center, edge devices or fog centers. How to make all these data points communicate effectively?

Solution - Given by OMG (Object Management Group)

An OMG standard known as the Distributed Data Service (DDS) defines a mechanism that allows data from sensors to flow upward through a hierarchy of edge and fog centers to applications using the data.

The DDS approach has the following characteristics:

Completely decentralized
Suitable for industrial use
Publish-Subscribe interactions
Flexible data handling capabilities
Support for an edge hierarchy

Completely decentralized

DDS avoids a single point of failure while minimizing latency by using direct communication

Suitable for industrial use.

DDS offers the high reliability needed for IIoT applications

It can be configured to meet performance requirements.

DDS offers the ability to authenticate control messages and encrypt data traffic.

Publish-Subscribe interactions.

DDS offers a publish-subscribe communication mechanism

Allows each application to choose the data the application will receive.

The applications can subscribe to only the data that is required.

Flexible data handling capabilities.

One subscriber may choose to receive all data while another chooses to receive only values beyond a specified threshold.

Support for an edge hierarchy.

DDS can be configured to form a distributed system.

It can have a hierarchy of cloud centers followed by fog centers and then to edge data center.

Databus

Databus provides interconnections among publishers and subscribers.
Databus is a communication abstraction implemented by software.
Software modules arrange to send messages between publishers and subscribers to meet requirements and optimize communication.
Databus technology includes a mechanism known as a gateway that allows a single Databus to span multiple levels of the hierarchy.
Rather than blindly sending a copy of every message, gateways perform a filtering function, and only forward a message to another level if one or more applications have subscribed to receive the message.

The following figure illustrates the functioning of DDS databus.