Java Programming

2013-01-06T20:45:00.000-08:00

If you are a beginner and looking for the Java tutorials to learn java programming language from scratch then this is the best place to start with the Java programming language.

Java programming language contains huge libraries that helps the programmer to develop any kind of applications. You can develop Desktop, web based, mobile and embedded device applications in the Java.

Java is platform independent programming language and can be run on any platform without recompiling. For example you can develop and compile the application on Windows machine and then deploy it on Linux on solaris os if there is JVM on the targeted system.

Start Now

Adapter Class

2012-04-20T20:29:00.000-07:00

Java provides adapter classes that implement the corresponding listener interface containing more than one method. The methods in the classes are empty. The listener class that you define can extend the Adapter class and override the methods that you need.

Example:

import java.awt.*;
import java.awt.event.*;

public class AdapterDemo
{
    public static void main(String[] args)
    {
        AdapterDemo1 d=new AdapterDemo1();
        d.setBounds(100,100,300,200);
        d.show();
    }
}
class AdapterDemo1 extends Frame
{
    public AdapterDemo1()
    {
        setTitle("Click close button to Quit");
        setSize(300, 200);
        setBackground(Color.gray);
        addWindowListener(
                new WindowAdapter()
                {
                    public void windowClosing(WindowEvent e)
                    {
                        System.exit(0);
                    }
                });
    }
}

Output:

Event Handling

2012-04-20T20:25:00.000-07:00

When the user clicks a button, types text or perform any other interface related action in your applet, an interface event occurs. Each component has a predefined set of events. When an event occurs in your applet, the applet notified and takes the appropriate action. In this case, you can find out what events – like mouse movements or button clicks – occurs as your applet runs by using the ActionListener interface.

In the java 1.0 the action() method is to handle the button clicks, but the action() method is now deprecated-obsolete. The new technique in java 1.1 and java 2 is the event delegation model.

In this event delegation model, if the event is irrelevant, it is discarded. The JDK 1.2 model is based on four components:

1. Event class

2. Event Listener

3. Explicit event Handling

4. Adapters.

The event delegation model works like this: Events are passed from source controls to listener objects. That means you will connect a listener to a button. So, when an event occurs object will “hear” it. This is accomplished by addActionListener() method.

Button1.addActionListener(this);

The this keyword refers the object you have currently in. Catch the events sent to you by overriding the actionperformed() method and adding your own version.

public void actionPerformed(ActionEvent ae)

{

}

The actionEvent object holds information about the event that occurred. Suppose you have many buttons in your applet. So, you can find which button is clicked by, using the getSource() method. This method returns the control that caused the event. The ActionListener and actionPerformed() are in java.awt.event.* package. You must first import the java.awt.event.* package for all event handling programs.

Example:

import java.awt.*;

import java.applet.*;

import java.awt.event.*;

public class ActionEventDemo extends Applet implements ActionListener

{

Button b;

public void init()

{

b=new Button("Click me");

add(b);

b.addActionListener(this);

}

public void actionPerformed(ActionEvent ae)

{

if(ae.getSource()==b)

b.setLabel("Clicked");

}

* <applet code="ActionEventDemo.class" width=200 height=100>

* </applet>

How to Execute this Example??

d:\> javac ActionEventDemo.java

d:\> appletviewer ActionEventDemo.java

Output:

List

2012-04-19T19:59:00.000-07:00

The list class allows you to create a scrolling list of values. The list can be set up so that the user can choose either one item or multiple items.

List(int number of rows visible, boolean multiple select mode)

To create a list, first create a constructor, and then populate the choice by repeatedly calling addItem().

Example:

import java.applet.*;

import java.awt.*;

public class ListDemo extends Applet

{

public void init()

{

List icecream=new List(3,true);

icecream.add("Chocolate");

icecream.add("Vennila");

icecream.add("Orange");

icecream.add("Mint chip");

icecream.add("Rum raisin");

add(icecream);

}

* <applet code="ListDemo.class" width=300 height=150>

* </applet>

How to Execute this Example??

d:\> javac ListDemo.java

d:\> appletviewer ListDemo.java

Output:

Choice

2012-04-19T19:53:00.000-07:00

A choice is a pull-down list. It is also called as combo box. The choice menu is used to display a list of choices for the user to select from. The choice menu is selected by mouse click on the choice control, alist of options drops down.

To create a choice, first create a constructor, and the populate the choice by repeatedly calling addItem().

int getItemCount() - returns the number of items in the choice menu.

void select(int position) - select the item at the given position.

String getItem(int index) - return the text of a given item.

Example:

import java.applet.*;

import java.awt.*;

public class ChoiceDemo extends Applet

{

public void init()

{

Choice color=new Choice();

color.add("Red");

color.add("Green");

color.add("Blue");

add(new Label("normal appearance"));

add(color);

}

* <applet code="ChoiceDemo.class" width=300 height=150>

* </applet>

How to Execute this Example??

d:\> javac ChoiceDemo.java

d:\> appletviewer ChoiceDemo.java

Output:

Check Box Group

2012-04-19T19:48:00.000-07:00

The checkbox group is also called as option button or radio button or exclusive check boxes. Check boxes are grouped together into check-box groups. So, only one member of a check box group is selected at a time. To use a check box group.

You first create an instance of CheckboxGroup and then pass the instance as a parameter to the Checkbox

constructor:

Checkbox cb=new CheckBox(String caption, group, state)

Here group refers the CheckboxGroup object

CheckboxGroup cbg=new CheckboxGroup();

Example:

import java.applet.*;

import java.awt.*;

public class CheckboxGroupDemo extends Applet

{

public void init()

{

setLayout(new GridLayout(3, 1));

CheckboxGroup cbg=new CheckboxGroup();

Checkbox cb1=new Checkbox("M.Sc", cbg,true);

Checkbox cb2=new Checkbox("M.C.A", cbg, false);

Checkbox cb3=new Checkbox("M.E", cbg, false);

add(cb1);

add(cb2);

add(cb3);

}

* <applet code="CheckboxGroupDemo.class" width=200 height=75>

* </applet>

How to Execute this Example??

d:\> javac CheckboxGroupDemo.java

d:\> appletviewer CheckboxGroupDemo.java

Output:

Check Box

2012-04-19T19:42:00.000-07:00

The Checkbox class is used to create a labelled check box. It has two parts a caption and state. The caption is text that represents the label of the control and the state is the boolean value(true/false).

By default the state is false which means the check box is unchecked.

Constructors:

Checkbox(String s)

Checkbox(String s,Initial state )

Methods:

getState() - returns the current state of the check box.

setState(boolean state) - It is used to set the state of check box.

Example:

import java.applet.*;

import java.awt.*;

public class CheckboxDemo extends Applet

{

public void init()

{

setLayout(new GridLayout(3, 1));

Checkbox c1=new Checkbox("Tamil", true);

Checkbox c2=new Checkbox("English");

Checkbox c3=new Checkbox("Maths");

add(c1);

add(c2);

add(c3);

}

* <applet code="CheckboxDemo.class" width=200 height=75>

* </applet>

How to Execute this Example??

d:\> javac CheckboxDemo.java

d:\> appletviewer CheckboxDemo.java

Output:

Text Area

2012-04-18T19:32:00.000-07:00

TextArea class handles the multiline of text. It is the subclass of TextComponent. The constructors for TextArea are Listed below:

TextArea() - It constructs an empty text area.

TextArea(String text) - It constructs a text area with text as initial context .

TextArea(int rows, int cols) - constructs an empty text area with the specified number of rows and columns.

TextArea(String text, int rows, int cols, int Scrollbarconstant) - constructs a text area whose initial content is text and the specified number of rows and columns with scrollbar. The scrollbar should be one of the following:

TextArea.SCROLLBARS_BOTH

TextArea.SCROLLBARS_NONE

TextArea.SCROLLBARS_HORIZONTAL_ONLY

TextArea.SCROLLBARS_VERTICAL_ONLY

append(String s) - this method is used to add the text at the end of a string in Text area.

insert(String s, int position) - to insert a text at particular position.

setEditable(boolean b) - Makes the text area editable, if true is passed as the argument.

Example:

import java.applet.*;

import java.awt.*;

public class TextAreaDemo extends Applet

{

public void init()

{

TextArea ta=new TextArea(5, 8);

Label l1=new Label("Text Area", Label.CENTER);

ta.setText("This\nis the \nTest\nfor Text Area\nwith\nnon editable \nmode");

add(l1);

add(ta);

ta.setEditable(false);

}

* <applet code="TextAreaDemo.class" width=250 height=150>

* </applet>

How to Execute this Example??

d:\> javac TextAreaDemo.java

d:\> appletviewer TextAreaDemo.java

Output:

Text Field

2012-04-18T19:27:00.000-07:00

To accept line of textual data from the user AWT provides TextField. It is the subclass of TextComponent. The Constructor for TextField are listed below:

TextField() - It constructs an empty text field.
TextField(String text) - It constructs a text field with the initial content is text.
TextField(int n) - Constructs an empty text field with the n number of columns.
TextField(String text, int n) - Constructs a text field whose initial content is text with n columns.

getText() - It returns the text content of the TextField.
setText() - It set the text for the TextField
setEchoChar(char c) – It allows you to specify an echo character for accepting password. If you have specified “*” as echo character. It displays the “*” in the text field instead of the text the user has keyed in.

Example:

import java.applet.*;
import java.awt.*;

public class TextFieldDemo extends Applet
{
public void init()
{
setLayout(new GridLayout(2, 2));
Label l=new Label("Enter the user Name",Label.CENTER);
TextField t1=new TextField();
Label l1=new Label("Enter your Password",Label.CENTER);
TextField t2=new TextField(10);
t2.setEchoChar('*');
add(l);
add(t1);
add(l1);
add(t2);
}
}

/*
* <applet code="TextFieldDemo.class" width=250 height=50>
* </applet>
*/

How to Execute this Example??

d:\> javac TextFieldDemo.java

d:\> appletviewer TextFieldDemo.java

Output:

Label

2012-04-18T19:17:00.000-07:00

The simplest AWT component is label. Labels do not respond to the user inputs, and they do not send any other events.

The following constructors are used to create a label.

Label()

Label(String caption)

Label(String caption, alignment)

The first constructor creates a empty label. The second one creates a specified text in the label. The default alignment to the label is left. The third constructor is used for creating a label with your alignment. The alignment values are:

Label.CENTER

Label.RIGHT

Label.LEFT

There are two methods supports the reading and setting text for the label.

getText() - It returns the text from the Label

setText() - It set the text for the Label

Example:

import java.applet.*;

import java.awt.*;

public class LabelDemo extends Applet

{

public void init()

{

setLayout(new GridLayout(2,1));

setBackground(Color.yellow);

Label l1=new Label("Java Programming");

Label l2=new Label("by surendranath Reddy",Label.CENTER);

add(l1);

add(l2);

}

</applet>

How to Execute this Example??

d:\> javac LabelDemo.java

d:\> appletviewer LabelDemo.java

Output:

Canvas

2012-04-18T18:51:00.000-07:00

A canvas is a component that has no default appearance or behavior. you can create canvas for custom drawing regions and work areas. It can receive input events from the mouse and the keyboard. You can use the setSize() method to make preferred size of the canvas.

Canvas()

Example:

import java.awt.*;

import java.applet.*;

public class CanvasDemo extends Applet

{

public void init()

{

setLayout(new FlowLayout(FlowLayout.RIGHT));

setBackground(Color.cyan);

Canvas c=new Canvas();

c.setBackground(Color.blue);

c.setSize(100,50);

add(c);

}

</applet>

How to Execute this Example??

d:\> javac CanvasDemo.java
d:\> appletviewer CanvasDemo.java

Output:

Insets

2012-04-17T18:38:00.000-07:00

If you want to leave a small space between the container that holds your components and the window that contains it. To do this, override the getInsets() method that is defined by the container.

Insets(int top, int left, int bottom, int right)

The values passed in top, left, bottom and right specify the amount of space between the container and its enclosing window.

Example:

import java.awt.*;
import java.applet.*;

public class InsetsDemo extends Applet
{

public void init()
{
setBackground(Color.cyan);
setLayout(new BorderLayout());
add(new Button("RMI"),BorderLayout.NORTH);
add(new Button("SERVLET"),BorderLayout.EAST);
add(new Button("JDBC"),BorderLayout.SOUTH);
add(new Button("BEANS"),BorderLayout.WEST);
add(new Button("JAVA"),BorderLayout.CENTER);
}

public Insets getInsets()
{
return new Insets(10,20,10,20);
}
}
/*
<applet code=”InsetsDemo.class” width=300 height=200>
</applet>
*/

How to Execute this Example??

d:\> javac InsetsDemo.java
d:\> appletviewer InsetsDemo.java

Output:

Border Layout

2012-04-17T18:34:00.000-07:00

The border layout manager provides you to position components using the directions North, South, East, West, Center. The middle area is called center.

The BorderLayout class has the following constructors:

BorderLayout()

BorderLayout(int horizontal, int vertical)

The first one create the default Border Layout. The second allows you to create border layout with horizontal and vertical space left between components.

Border layout class have five constraints. These are used in adding components in the container.

BorderLayout.EAST

BorderLayout.WEST

BorderLayout.NORTH

BorderLayout.SOUTH

BorderLayout.CENTER

public void add(Component c, Constraint c1)

Example:

import java.awt.*;

class BorderDemo extends Frame

{

BorderDemo(String s)

{

super(s);

setSize(300,140);

add(new Button(“North”),BorderLayout.NORTH);

add(new Button(“East”),BorderLayout.EAST);

add(new Button(“South”),BorderLayout.SOUTH);

add(new Button(“West”),BorderLayout..WEST);

add(new Button(“Center”),BorderLayout.CENTER);

setVisible(true);

}

class test2

{

Public static void main(String[] args)

{

BorderDemo bd=new BorderDemo(“Border Layout”);

}

Grid Layout

2012-04-17T09:30:00.000-07:00

The grid layout manager organizes the display into a rectangular grid. It places the components into left to right and top to bottom. The grid layout class has the following constructors:

GridLayout(int rows, int cols)

This constructs a grid layout with the specified number of rows and columns. All the components are of equal size. This is mostly used to specify that the components are of equal size. The following program place the buttons in 3 rows and 4 columns using GridLayout.

Example:

import java.awt.*;

class GridDemo extends Frame

{

GridDemo(String s)

{

super(s);

setSize(300,140);

setLayout(new GridLayout(3,4));

for(int i=0 ; i<=12 ; i++)

add(new Button(“Button no”+i));

setVisible(true);

}

Class test1

{

public static void main(String[] args)

{

GridDemo gd=new GridDemo(“Grid layout”);

}

The following program illustrate the stating point of 8 square puzzle problem.

import java.awt.*;

public class eight extends java.applet.Applet;

{

public void init()

{

setLayout(new GridLayout(3,3));

setFont(new Font(“SansSerif”,Font.PLAIN,24));

for(int i=0 ; i<3 ; i++)

{

for(int j=0 ; j<3 ; j++)

{

int number=i*3+j;

if(number>0)

add(new Button(“”+number));

}

</applet>

Flow Layout

2012-04-17T06:18:00.000-07:00

The FlowLayout arrange the components from upper left corner, left to right and top to bottom. When no more components fit on a line, the next one appears on the next line. A small space is left between every component on each side.

Constructors of FlowLayout:

FlowLayout()
FlowLayout(int align)
FlowLayout(int align, int horizontal, int vertical)

The first form creates a default layout, which centers components and leaves five pixels of space between components.
The second one uses the following alignment constants. They align the components left, center and right respectively.

FlowLayout.LEFT
FlowLayout.CENTER
FlowLayout.RIGHT

The third form in addition to specify the vertical and horizontal space between the components.

Example:

import java.awt.*;
class Fl extends Frame
{
   Fl(String s)
   {
   super(s);
   setSize(300,140);
setLayout(new FlowLayout());
for(int i=0 ; i<=9 ; i++)
add(new Button(“Button No”+i));
setVisible(true);
   }
}
class test
{
Public static void main(String[] args)
{
Fl=new Fl(“Flow Layout”);
}
}

The following applet program use the second type of FlowLayout constructor and the alignment value is LEFT. Try yourself to change the alignment Center and Right.

Example:

import java.awt.*;
import java.applet*;

public class Left extends Applet
{
Button b1,b2,b3;
      Public void init()
{
setLayout(new FlowLayout(FlowLayout.LEFT));
b1=new Button(“One”);
b2=new Button(“Two”);
b3=new Button(“Three”);
add(b1);
add(b2);
add(b3);
}
}

/*
<applet code=”Left.class” width=300 height=200>
</applet>
*/

Layout Managers

2012-04-17T06:10:00.000-07:00

The arrangement of several components within a container is called their layout. java components borrow their behaviour from the window. The Button, TextBox and other components have different size when instantiated on different platforms. Suppose you have to create a button on your application. The application runs on windows 95 machine, this button will be 32 pixels wide and 21 pixels height. Pixel(picture element) is a small graphical unit. On a Motif platform button will be 32 pixels wide and 22 pixels height, even though it uses the same font. Java solve the problem by using the Layout manager.

Java defines the five layout classes FlowLayout, GridLayout, BorderLayout, CardLayout and GridBagLayout. These are all subclass of the java.awt.LayoutManager class. You can set the layout by using the setLayout() method.

Notes 1: A panel’s default layout manager is always FlowLayout
2: An applet’s default layout manager is always FlowLayout and constraint is
FlowLayout.CENTER
3: A frame’s default layout manager is always BorderLayout.

Frame

2012-04-16T22:34:00.000-07:00

The Frame class provides windows for Applets and Applications. The following program illustrates the frame.

Example:

import java.awt.*;

class frameDemo

{

Public static void main(String[] args)

{

Frame f=new Frame(“This is my frame”);

f.setBackground(Color.red);

f.setSize(300,300);

f.setVisible(true);

System.out.println(“Return to DOS prompt and press control+c to quit”);

}

Explanation:

In the above program we created a frame, and set the title as “This is my frame”. To determine the size of frame by setSize() method and set the Background color by setBackground() method. The size is 300 pixels wide and 100 pixel high. The frame invoke the setVisible() method to display the frame window.

The frame cannot be destroyed directly. So come to DOS prompt and press control+C to quit.

The above program can be written as follows

import java.awt.*;

class myFrame extends Frame

{

myFrame()

{

super(“This is my frame”);

setBackground(Color.red);

setSize(300,300);

setCursor(Frame.HAND_CURSOR);

show();

}

public static void main(String[] args)

{

new myFrame();

System.out.println(“Return to DOS prompt and press ctrl+C to quit”);

}

output:

The frame class consist of a method setCursor(int), it is used to set type of cursor. The cursor must be in one of the following type. It is deprecated method.

DEFAULT_CURSOR

TEXT_CURSOR

SW_RESIZE_CURSOR

NW_RESIZE_CURSOR

N_RESIZE_CURSOR

W_RESIZE_CURSOR

HAND_CURSOR

NORMAL

CROSSHAIR_CURSOR

WAIT_CURSOR

SE_RESIZE_CURSOR

NE_RESIZE_CURSOR

S_RESIZE_CURSOR

E_RESIZE_CURSOR

MOVE_CURSOR

ICONIFIED

Component

2012-04-16T22:30:00.000-07:00

A component is an object that can be displayed on the screen and can interact with the user. It is like a button or a scroll bar, that has a visual representation in a screen window. Component have special properties including background color and font.

Intro

2012-04-16T22:26:00.000-07:00

The Abstract Window Toolkit (AWT) is a library of java packages that forms a part of the java API. It includes over 25 packages that define hundreds of classes used for Graphical User Interface (GUI). The AWT classes contained in the java.awt package. The following diagram illustrate the component hierarchy.

This package provides an integrated set of classes to manage user interface components like windows, dialog boxes, button, checkbox, lists, menus, scrollbars and text fields. The Component class, which implements the common functionality, is the super class for all GUI elements.

Every component has a unique container that directly contains it. A container is a window like component that can contain other components. It has special properties, including layout manager and insets. It is a sub class of Component.

A window class creates a top-level window. It sits directly on the desktop. It is a subclass of container.

A Frame is a subclass of Window and has a title bar, menu bar, a cursor and an icon image.

Button Class

2012-04-16T02:33:00.000-07:00

A button is a component that has a label and can respond when pressed.

Button() - Construct a button with no label

Button(String label) - Construct a button with specified label

Methods

setLabel(String label) – It sets the label to the specified string

getLabel() - Gets the label from the button.

Example:

import java.awt.*;

class frameDemo

{

public static void main(String[] args)

{

Button b;

Frame f=new Frame(“Button Demo”);

f.setSize(250,150);

b=new Button(“Click me”);

f.add(b);

f.setLocation(200,200);

f.setVisible(true);

System.out.println(“Return to DOS prompt and press ctrl+C to quit”);

}

output:

The setLocation(int x, int y) – This method displays frame located upper left corner at x,y.

The add() method adds the button to the frame.

Note: Button fills the entire Frame. Because, A frame’s default Layout manager is always Border Layout and its default constraint is BorderLayout.CENTER.

java.util

2012-04-13T05:45:00.001-07:00

The Java Collections Framework has a data structure that should work for virtually anything you'll ever need to do. Want to keep a list that you can easily keep adding to? Want to find something by name? Want to create a list that automatically takes out all the duplicates? Sort your co-workers by the number of times they've stabbed you in the back? Sort your pets by number of tricks learned? It’s all here...

TreeSet

Keeps the elements sorted and prevents duplicates.

HashMap

Let's you store and access elements as name/value pairs.

LinkedList

Designed to give better performance when you insert or delete elements from the middle of the collection. (In practice, an ArrayList is still usually what you want.)

HashSet

Prevents duplicates in the collection, and given an element, can find that element in the collection quickly.

LinkedHashMap

Like a regular HashMap, except it can remember the order in which elements (name/value pairs) were Inserted, or it can be configured to remember the order in which elements were last

accessed.

The java.util package contains classes and interfaces that are useful for working with groups of objects.

The package also contains classes that are used to develop applications to manipulate date, time, and generating random numbers and so on.

It also contains a list of classes and interfaces to manage a collection of data in memory.

               Collections Framework
               Collection Interface
               List Interface
               ArrayList class
               Vector class
               LinkedList class
               Set Interface
               HashSet class
               TreeSet class
               Map Interface
               HashTable class
               HashMap class
               TreeMap class
               Stack class

Stack Class

2012-04-13T05:27:00.001-07:00

Extends the Vector class. Used to create a simple last-in-first-out stack.

· An item is stored on a stack by ‘pushing’ it into the stack.

· An item may subsequently be ‘popped’ off the stack and used.

· A Stack object will grow in size as new items are pushed onto it.

Example:

import java.util.EmptyStackException;

import java.util.Stack;

public class StackDemo {

Stack s;

    public StackDemo()
    {
      s = new Stack();
    }

public static void main(String args[])
{

StackDemo objStackDemo = new StackDemo();

objStackDemo.pushItem("Harry");

objStackDemo.pushItem("Emaini");

objStackDemo.pushItem("Voldmort");

objStackDemo.pushItem("Snape");

objStackDemo.pushItem("Dumbuldore");

System.out.println();

objStackDemo.popItem();

try
{

objStackDemo.popItem();

} catch(EmptyStackException e) {

System.out.println("Exception : Empty Stack");

}

void pushItem(String str)
{

s.push(str);

System.out.println("Pushed : " + str);

System.out.println("Stack has : " + s);

}

void popItem()
{

String str = (String)s.pop();

System.out.println("Popped : " + str);

System.out.println("Stack has : " + s);

}

Queue Interface

public interface Queue extends Collection

– A collection designed for holding elements prior to processing.

– Queues typically order elements in a FIFO (first-in-first-out) manner.

– In a FIFO queue, all new elements are inserted at the tail of the queue.

TreeMap Class

2012-04-13T05:25:00.001-07:00

public class TreeMap extends AbstractMap implements SortedMap, Cloneable,Serializable

The TreeMap class implements the SortedMap interface (and thus the Map interface too), but stores elements in a tree structure. The treeMap returns keys in sorted order.

Constructory

TreeMap() Constructs a new, empty map, sorted according to the keys' natural order

TreeMap(Comparator c) Constructs a new, empty map, sorted according to the given comparator.

TreeMap(Map m) Constructs a new map containing the same mappings as the given map, sorted according to the keys' natural order.

TreeMap(SortedMap m) Constructs a new map containing the same mappings as the given SortedMap, sorted according to the same ordering.

Some Important Methods
Object	firstKey() Returns the first (lowest) key currently in this sorted map.
SortedMap	headMap(Object toKey) Returns a view of the portion of this map whose keys are strictly less than toKey.
Object	lastKey() Returns the last (highest) key currently in this sorted map.
SortedMap	tailMap(Object fromKey) Returns a view of the portion of this map whose keys are greater than or equal to fromKey.

Example:

import java.util.HashMap;

import java.util.Map;

import java.util.TreeMap;

public class TreeMapDemo
{

public static void main(String[] args)
{

if(args.length < 1)
{

System.out.println("Usage : java WordsCount <sample string>");

System.exit(0);

}

Map WordList = new HashMap();

for(int count = 0;count < args.length; count++)
{

// Get the next word

String key = args[count];

// Get the frequency of the word

// referred by "key"

Integer frequency = (Integer)WordList.get(key);

/* If the word does not exists in the map

then initialize frequency to 1

else increment it by 1

if(frequency == null)
{

frequency = new Integer(1);

        }
        else
        {

int value = frequency.intValue();

frequency = new Integer(value + 1);

}

// Update the frequency for the word

// referred by "key"

WordList.put(key, frequency);

}

// Display the words and its

// corresponding frequency

Map sortedWordList = new TreeMap(WordList);

System.out.println(sortedWordList);

}

HashMap Class

2012-04-13T05:24:00.001-07:00

public class HashMap extends AbstractMap implements Map

Hash table based implementation of the Map interface. This implementation provides all of the optional map operations, and permits null values and the null key. (The HashMap class is roughly equivalent to Hashtable, except that it is unsynchronized and permits nulls.) This class makes no guarantees as to the order of the map; in particular, it does not guarantee that the order will remain constant over time.

Constructor

HashMap() Constructs an empty HashMap with the default initial capacity (16) and the default load factor (0.75).

HashMap(int initialCapacity) Constructs an empty HashMap with the specified initial capacity and the default load factor (0.75).

HashMap(int initialCapacity, float loadFactor) Constructs an empty HashMap with the specified

initial capacity and load factor.

HashMap(Map<? extends K,? extends V> m) Constructs a new HashMap with the same mappings

as the specified Map.

Example:

import java.util.*;

class Hashtest

{

public static void main(String args[])

{

Hashtable ht = new Hashtable();

Enumeration enume;

String strName;

ht.put("Tony",new String("2001"));

ht.put("Cathy",new String("2002"));

ht.put("Michael",new String("2002"));

ht.put("Priscilla",new String("2001"));

ht.put("Mark",new String("2001"));

enume = ht.keys();

while(enume.hasMoreElements())

{

strName = (String)enume.nextElement();

System.out.println(strName + " completed graduation in " +

ht.get(strName) + "\n");

}

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