Dev Blog No. 1

Abstract Class Vs Interface

2021-06-07T21:30:00.002+05:30

Interface

Completely "abstract class", which can only contain abstract methods and properties (with empty bodies).
By default, members of are abstract and public.
Can contain properties and methods, but not fields.
The body must be provided by the "derived" class without using override keyword.
Virtual method is not allowed in interface.
Cannot contain a constructor.
Multiple inheritance can achieved.
It can't be instantiate.

Abstract Class

It is Restricted class, that cannot be instantiate.
To access it, it must be inherited from another class.
Typically used to define a base class in the class hierarchy.
An abstract class can have both abstract and regular methods.

Wrong

This class must contain at least one abstract method.
Abstract classes are either partially implemented or not implemented at all.

eg.

public interface IInterface // sealed, private, protected, protected internal are not possible, public is optional (by default public)
{

void demo();
void demo1();
}

public class InterfaceDemoTest : IInterface

{

public void demo()

{

Console.WriteLine("Demo Method Called");

}

public void demo1()

{

Console.WriteLine("Demo1 Method Called");
}
}

public abstract class AbstractClass // sealed, private, protected, protected internal are not possible

{

int x, y;

public AbstractClass()

{

Console.WriteLine("Abstract Constructor Called");

}

// Abstract method

// Without abstract method is also possible

public abstract void demo();

// Concrete method

public virtual void demo1()

{

Console.WriteLine("Non-Abstract Parent Method Called");

}

public class AbstractDemoTest: AbstractClass

{

public override void demo()

{

Console.WriteLine("Abstract Method Called");

AbstractClass abs = new AbstractDemoTest(); // new AbstractClass() is not possible

}

class Program

{

static void Main(string[] args)

{

AbstractDemoTest abstractDemoTest = new AbstractDemoTest();

abstractDemoTest.demo();

abstractDemoTest.demo1();

InterfaceDemoTest interfaceDemoTest = new InterfaceDemoTest();

interfaceDemoTest.demo();

interfaceDemoTest.demo1();

IInterface iinterface = new InterfaceDemoTest();

iinterface.demo();

iinterface.demo1();

Console.ReadLine();

}

}

Difference between Abstract class and Interface
Abstract	Interface
Can have abstract and regular(concrete) methods both	Can have only abstract methods without abstract keyword
Can have Constructor	Can’t have Constructor
Can create object as reference to child class AbstractClass abs = new AbstractDemoTest();	Can create object as reference to child class IInterface iinterface = new InterfaceDemoTest();
By default private class	By default public interface
Access modifiers required for methods	Access modifiers not required for methods
Multiple inheritances can’t achieve.	Multiple inheritances can achieve.
Can contain fields	Can’t contain fields
Only Abstract methods must be implement in derived class	All methods must be implement in derived class
Used for inheritance	Used for inheritance

Similarities between Abstract class and Interface

Can’t Create Instance

Abstract methods must me implement in derived class

Used for inheritance

Used as Parent in inheritance

Test Cafe

2021-05-27T14:34:00.001+05:30

What is Test Cafe

Allows you to write tests using TypeScript or JavaScript
End-to-end free and open source automation tool which is used to test web applications
Works on all popular environments such as Windows, MacOS, and Linux
Easy to install feature in a single command
Does not depend on Selenium or other testing software

How to Install

npm install -g testcafe

Sample Program

import { Selector } from 'testcafe';

fixture `Getting Started`// declare the fixture

.page `https://devexpress.github.io/testcafe/example`; // specify the start page

//then create a test and place your code there

test('My first test', async t => {

await t

.wait(2000)

.typeText('#developer-name', 'John Smith')

.click('#submit-button')

// Use the assertion to check if the actual header text is equal to the expected one

.expect(Selector('#article-header').innerText).eql('Thank you, John Smith!')

.wait(2000);

});

How to Run

testcafe chrome test1.js

Fiture: TestCafe tests are organized into categories called fixuture. Fixture can be compared with Module where test cases related to similar functionalities are maintained.

Declare Fixture

fixture ( fixtureName )

fixture `fixtureName`

Test: test case/functionality to be verified

test ( 'testName', fn(t))

Test Controller: object t exposes the test API's methods. Thus it is passed to each function.

Page can be written in two ways

1. fixture `fixtureName`

.page `PageUrl`;

2. test

.page `PageUrl`

('testName', fn(t));

Actions

Browser

Returns information about the current user agent: the operating system, platform type, browser, engine, etc.

Syntax:

t.browser

eg.

if (t.browser.name !== 'Chrome')

await t.expect(Selector('div').withText('Browser not supported').visible).ok();

ClearUpload

Removes all file paths from the specified file upload input.

Syntax:

t.clearUpload(selector)

eg.

.setFilesToUpload('#upload-input', [

'./uploads/1.jpg',

'./uploads/2.jpg',

'./uploads/3.jpg'

])

.clearUpload('#upload-input')

OpenWindow

Opens a new browser window.

Syntax:

t.openWindow( url )

eg.

.openWindow('http://devexpress.github.io/testcafe')

.openWindow('./documentation');

CloseWindow

Closes a browser window. Each call of the t.closeWindow method closes the active window:

Syntax:

t.closeWindow([windowDescriptor])

eg.1

t.openWindow('https://devexpress.github.io/testcafe');

.openWindow('https://devexpress.com');

.closeWindow()

.closeWindow();

eg.2

const testcafe = await t.openWindow('https://devexpress.github.io/testcafe');

await t.openWindow('https://devexpress.com');

const devexpress = await t.getCurrentWindow();

await t.closeWindow(devexpress)

.closeWindow(testcafe);

Debug

Pauses the test and allows you to use the browser’s developer tools.

Syntax:

t.debug()

eg.

.debug()

DoubleClick

Double-clicks an element on a page.

Syntax:

t.doubleClick(selector [, options])

eg.

const dialog = Selector('#dialog');

.doubleClick('#thumbnail')

.expect(dialog.visible).ok();

Drag

Drags an element to a specified offset.

Syntax:

t.drag(selector, dragOffsetX, dragOffsetY [, options])

eg.

.drag('.ui-slider-handle', 360, 0, { offsetX: 10, offsetY: 10 })

.expect(slider.value).eql(7);

DragToElement

Drags an element onto another web page element.

Syntax:

t.dragToElement(selector, destinationSelector [, options])

eg.

const designSurfaceItems = Selector('.design-surface').find('.items');

.dragToElement('.toolbox-item.text-input', '.design-surface')

.expect(designSurfaceItems.count).gt(0);

Eval

Creates a client function and executes it immediately (without saving).

Always place eval in a separate call.

Syntax:

t.eval(fn [, options])

eg.1

const docURI = await t.eval(() => document.documentURI);

eg.2

await t.eval(() => location.reload(true));

Expect

This method accepts the actual value.

Syntax:

await t.expect(doSomethingAsync()).ok('check that a promise is returned', { allowUnawaitedPromise: true });

eg.1

.expect(developerNameInput.value).eql('', 'input is empty')

eg.2

.expect(developerNameInput.value).notEql('', 'input is empty')

eg.3

.expect(developerNameInput.value).contains('Peter', 'input contains text "Peter"');

eg.4

.expect(Selector('#element').exists).ok();

eg.5

.expect(Selector('#element').exists).notOk();

eg.6

.expect(Selector('#element').getAttribute('attr')).typeOf('string');

eg.7

.expect(Selector('#element').getAttribute('attr')).typeOf('string');

eg.8

.expect(Selector('#element').clientWidth).gt(300);

eg.9

.expect(Selector('#element').clientWidth).gte(300);

eg.10

.expect(Selector('#element').clientWidth).lt(300);

eg.11

.expect(Selector('#element').clientWidth).lte(300);

eg.12

.expect(Selector('#element').scrollTop).within(300, 400);

eg.13

.expect(Selector('#element').scrollTop).within(300, 400);

eg.14

.expect(developerNameInput.value).match(/\.com/);

eg.15

.expect(developerNameInput.value).notMatch(/\.com/);

getBrowserConsoleMessages

Returns messages posted to the browser console. Cannot be chained with other methods of the test controller.

Syntax:

t.getBrowserConsoleMessages()

eg.

// check-prop-types.js

import { t } from 'testcafe';

export default async function () {

const { error } = await t.getBrowserConsoleMessages();

await t.expect(error[0]).notOk();

}

// test.js

import { Selector } from 'testcafe';

import checkPropTypes from './check-prop-types';

fixture `react example`

.page `http://localhost:8080/` // https://github.com/mzabriskie/react-example

.afterEach(() => checkPropTypes());

test('test', async t => {

await t

.typeText(Selector('.form-control'), 'devexpress')

.click(Selector('button').withText('Go'))

.click(Selector('h4').withText('Organizations'));

});

Note: This method can be used with below fields

error (Array of String) Error messages printed in the console.

warn (Array of String) Warning messages printed in the console.

log (Array of String) Log messages printed in the console.

info (Array of String) Information messages printed in the console.

getCurrentWindow

Retrieves a window descriptor that corresponds to the active window.

Syntax:

t.getCurrentWindow()

eg.

await t.openWindow('https://devexpress.com');

const devexpress = await t.getCurrentWindow();

await t.closeWindow(devexpress);

hover

Hovers the mouse pointer over a web page element.

Syntax:

t.hover(selector [, options])

eg.

const comboBox = Selector('.combo-box');

.hover(comboBox)

maximizeWindow

Maximizes the browser window.

Syntax:

t.maximizeWindow()

eg.

.maximizeWindow()

navigateTo

Navigates to the specified URL.

Syntax:

t.navigateTo(url)

eg.

.navigateTo('http://devexpress.github.io/testcafe')

.navigateTo('file:///user/my-website/index.html')

.navigateTo('../my-project/index.html')

openWindow

Opens a new browser window.

Syntax:

eg.

t.openWindow( url )

.openWindow('http://devexpress.github.io/testcafe')

.openWindow('./documentation');

pressKey

Presses the specified keyboard keys.

Syntax:

t.pressKey(keys [, options])

eg.

.pressKey('h o m e home r i g h t right r i g h t right',{ speed: 0.1 })

.pressKey('ctrl+a d e v 1 s p a c e space b a c k s p a c e backspace ctrl+a',{ speed: 1 })

.pressKey('ctrl+a D E V 2 e n d end l e f t left c t r l + a ctrl+a delete a a a a backspace delete',{ speed: 1 })

.pressKey('ctrl+a backspace',{ speed: 1 })

Below are the various actions we can perform by using presskey

'backspace'
'tab'
'enter'
'capslock'
'esc'
'space'
'pageup'
'pagedown'
'end'
'home'
'left'
'right'
'up'
'down'
'ins'
'delete'

option: speed valued can be between 0.01 to 1

resizeWindow

Resizes a window to fit the parameters entered by user

Syntax

t.resizeWindow(width, height)

eg.

.resizeWindow(200, 100)

resizeWindowToFitDevice

Resizes the window to fit the screen of the specified mobile device.

Syntax

t.resizeWindowToFitDevice(deviceName [, options])

eg.

.resizeWindowToFitDevice('Sony Xperia Z', {

portraitOrientation: true

})

Remark

device name is configured in viewport-sizes.json file like below

"sonyxperiaz": {

"portraitWidth": 360,

"landscapeWidth": 640,

"name": "Sony Xperia Z"

All list of device name

https://github.com/DevExpress/device-specs/blob/master/viewport-sizes.json

rightClick

Right-clicks an element on a page.

Syntax

t.rightClick(selector [, options])

eg.

.rightClick('#cell-1-1')

scroll

Scrolls the target element to a specified position. If no target is specified, the document body is scrolled.

Syntax

t.scroll([target,] posX, posY[, options])

and

t.scroll([target,] position[, options])

eg.

const container = Selector('#container');

.scroll(container, 'bottomRight');

scrollBy

Scrolls the target element by the specified number of pixels. If no target is specified, the document body is scrolled.

Syntax

t.scrollBy([target,] x, y[, options])

eg.

.scrollBy(500, -200);

scrollIntoView

Scrolls parent containers of the target element until the element is in the viewport.

Syntax

.scrollIntoView(target [, options])

eg.

const target = Selector('#target');

.scrollIntoView(target);

selectEditableContent

Selects editable content on a web page.

Syntax

t.selectEditableContent(startSelector, endSelector [, options])

eg.

.selectEditableContent('#foreword', '#chapter-3')

selectText

Selects text in input elements of various types.

Syntax

t.selectText(selector [, startPos] [, endPos] [, options])

eg.

const developerNameInput = Selector('#developer-name');

.selectText(developerNameInput, 7, 1);

selectTextAreaContent

Selects <textarea> content.

Syntax

t.selectTextAreaContent(selector [, startLine] [, startPos] [, endLine] [, endPos] [, options])

eg.

const commentTextArea = Selector('#comments');

.selectTextAreaContent(commentTextArea, 0, 5, 2, 10);

setFilesToUpload

Sets files to upload. Emulates a user’s selection in the browser’s ‘Choose File’ dialog.

Syntax

t.setFilesToUpload(selector, filePath)

eg.

.setFilesToUpload('#upload-input', [

'./uploads/1.jpg',

'./uploads/2.jpg',

'./uploads/3.jpg'

])

.click('#upload-button');

setPageLoadTimeout

Defines the time passed after the DOMContentLoaded event within which the window.load event should be raised.

Syntax

t.setPageLoadTimeout(duration)

eg.

.setPageLoadTimeout(0)

setTestSpeed

Specifies the test execution speed.

Syntax

t.setTestSpeed(factor)

eg.

.setTestSpeed(0.1)

switchToIframe

Switches to an <iframe>.

Syntax

t.switchToIframe(selector)

eg.

.switchToIframe('#iframe-1')

switchToMainWindow

Switches the test’s browsing context from an <iframe> back to the main window.

Syntax

t.switchToMainWindow()

eg.

.switchToIframe('#iframe-1')

.click('#button-in-iframe-1')

.switchToMainWindow()

.click('#button-in-main-window');

switchToParentWindow

Activates the window that launched or was active when the active window was launched.

Syntax

t.switchToParentWindow()

eg.

.openWindow('https://devexpress.com')

.switchToParentWindow();

switchToPreviousWindow

Activates the previously active window.

Syntax

t.switchToPreviousWindow()

eg.

.openWindow('https://devexpress.com')

.switchToPreviousWindow();

switchToWindow

Switches to a specific browser window.

Syntax

t.switchToWindow(windowDescriptor)

t.switchToWindow(filterFn)

eg.

const homepage = await t.getCurrentWindow();

const documentation = await t.openWindow('http://devexpress.github.io/testcafe/documentation');

await t.switchToWindow(homepage)

.switchToWindow(documentation);

takeElementScreenshot

Takes a screenshot of the specified page element.

Syntax

t.takeElementScreenshot(selector[, path][, options])

eg.

.takeElementScreenshot(Selector('fieldset').nth(1), 'my-fixture/important-features.png')

takeScreenshot

Takes screenshot of the entire page.

Syntax

t.takeScreenshot([options])

eg.

.takeScreenshot({

path: 'my-fixture/thank-you-page.png',

fullPage: true

});

typeText

Types the specified text into an input element.

Syntax

t.typeText(selector, text [, options])

eg.

.typeText(nameInput, 'Peter')

.typeText(nameInput, 'Paker', { replace: true })

.typeText(nameInput, 'r', { caretPos: 2 })

.typeText(color, '#FF8040')

.typeText(datetime, '2017-11-03T05:00')

.typeText(date, '2017-11-03')

.typeText(time, '15:30')

.typeText(month, '2017-08')

.typeText(range, '80');

useRole

Activates the role.

Syntax

t.useRole(role)

eg.

const registeredUser = Role('http://example.com/login', async t => {

await t

.typeText('#login', 'username')

.typeText('#password', 'pa$$w0rd')

.click('#sign-in');

});

test('My Test', async t => {

await t

.useRole(registeredUser)

.expect(Selector('#avatar').visible).ok();

wait

Pauses a test for a specified period of time.

Syntax

t.wait(timeout)

eg.

.wait(1000)

SQL Queries Interview Questions

2021-05-16T17:31:00.024+05:30

Q1. Second Highest salary of employee

select

distinct top 1 *

from

employees

where

Salary < (Select MAX(Salary) from employees)

order by Salary desc

select

distinct top 1 *

from

employees

where

Salary < (Select distinct top 1 salary from employees order by Salary desc)

order by Salary desc

Select

top 1 *

from (

Select distinct top 2 *

from

employees

order by Salary desc

) innerQuery

order by salary asc

Select emp.*

from (

Select *, row_number() OVER (Order by salary desc

) as rn from employees) innerQuery

inner join employees emp on emp.id = innerQuery.id

where innerQuery.rn =2

Q2. Select Third Highest Data

select

distinct top 1 *

from

(Select distinct top 3 * from employees order by salary desc) innerQuery

order by salary asc

Q3. Select Duplicate Data

Select *

from employees

where salary in

(

Select salary from employees group by salary having count(salary) > 1

)

order by salary desc

select employees.*

from

(

select max(emp1.id) empId

from employees emp1

inner join employees emp2

on emp1.salary = emp2.salary

and emp1.id <> emp2.id

group by emp1.salary

) innerQuery

inner join employees

on innerQuery.empId = employees.id

order by employees.id

Q4. Delete Duplicate Data

Delete

from employees

where id in (

Select max(id) from employees group by salary having count(salary) > 1

)

Delete employees

from

(

select max(emp1.id) empId

from employees emp1

inner join employees emp2

on emp1.salary = emp2.salary

and emp1.id <> emp2.id

group by emp1.salary

) innerQuery

inner join employees

on innerQuery.empId = employees.id

Q5. Fetch monthly salary if annual salary is given

Select *, salary/12 as monthlySalary from employees

Q6. How to fetch top 3 highest salary

select * from

(Select *, row_number() over (order by salary desc) rn from employees) innerQuery

where innerQuery.rn <=3

select top 3 * from employees order by salary desc

Q7. Select employee details having odd id

select * from employees where id%2=1

Q8. Select employee details having even id

select * from employees where id%2=0

Q9. How Can I create table with same structure of table without data

select * into NEW_TABLE from EXISTING_TABLE where 1=2

Q10. How Can I create table with same structure of table with data

select * into NEW_TABLE from EXISTING_TABLE

Q11. Display last 50% records from Employee table

select * from

(Select *,row_number() over(order by id) rn from employees) innerQuery

where innerQuery.rn >= (select count(id)/2 from employees)

Q12. How do I fetch only common records between 2 tables

select * from employees

intersect

select * from employees_new

Q13. Find Query to get information of Employee where Employee is not assigned to the department

select * from employees where deptid not in (select id from department)

select * from employees

except

select emp.* from employees emp

inner join department dep

on emp.deptid = dep.Id

select emp.* from employees emp

left join department dep

on emp.deptid = dep.Id

where dep.Id is null

Q14. How to get distinct records from the table without using distinct keyword.

select * from employees where id in (select max(id) from employees group by FirstName, LastName)

Q15. Select all records from Employee table whose name is ‘Jitendra’ and ‘Ram’

select * from employees where FirstName in ('Jitendra', 'Ram')

Q16. How to fetch all the records from Employee whose joining year is 2017

select * from employees where substring(convert(varchar,DOJ,103),7,4)='2017'

select * from employees where DOJ like '2017%'

Q17. What is SQL Query to find maximum salary of each department?

select max(emp.Salary), dep.DepartmentName from employees emp

inner join department dep

on emp.deptid = dep.Id

group by dep.DepartmentName

select max(emp.Salary), emp.deptid from employees emp group by emp.deptid

Q18. How Do you find all Employees with its managers?

select emp.FirstName + ' ' + emp.LastName as EmpName, manager.FirstName + ' ' + manager.LastName as ManagerName

from employees emp, employees manager

where emp.ManagerId = manager.id

select emp.FirstName + ' ' + emp.LastName as EmpName, manager.FirstName + ' ' + manager.LastName as ManagerName

from employees emp

inner join employees manager

on emp.ManagerId = manager.id

Q19. How to find count of duplicate rows

select FirstName, count(FirstName) cnt from employees group by FirstName, LastName, Location having count(FirstName) > 1

Q20. How to Find the Joining date of Employee in YYYY-DAY-Date format.

select SUBSTRING(CONVERT(VARCHAR, DOJ, 121), 1, 4) + '-' + SUBSTRING(CONVERT(VARCHAR, DOJ, 100), 1, 3) + '-' + SUBSTRING(CONVERT(VARCHAR, DOJ, 103), 1,2) from employees

Q20. Display current date in different format

select CONVERT(VARCHAR, GETDATE(), 100) '100'

select CONVERT(VARCHAR, GETDATE(), 101) '101'

select CONVERT(VARCHAR, GETDATE(), 102) '102'

select CONVERT(VARCHAR, GETDATE(), 103) '103'

select CONVERT(VARCHAR, GETDATE(), 104) '104'

select CONVERT(VARCHAR, GETDATE(), 105) '105'

select CONVERT(VARCHAR, GETDATE(), 106) '106'

select CONVERT(VARCHAR, GETDATE(), 107) '107'

select CONVERT(VARCHAR, GETDATE(), 108) '108'

select CONVERT(VARCHAR, GETDATE(), 109) '109'

select CONVERT(VARCHAR, GETDATE(), 110) '110'

select CONVERT(VARCHAR, GETDATE(), 111) '111'

select CONVERT(VARCHAR, GETDATE(), 112) '112'

select CONVERT(VARCHAR, GETDATE(), 113) '113'

select CONVERT(VARCHAR, GETDATE(), 114) '114'

select CONVERT(VARCHAR, GETDATE(), 120) '120'

select CONVERT(VARCHAR, GETDATE(), 121) '121'

select CONVERT(VARCHAR, GETDATE(), 126) '126'

select CONVERT(VARCHAR, GETDATE(), 127) '127'

select CONVERT(VARCHAR, GETDATE(), 130) '130'

select CONVERT(VARCHAR, GETDATE(), 131) '131'

Output

May 16 2021 10:41PM

05/16/2021

2021.05.16

16/05/2021

16.05.2021

16-05-2021

16 May 2021

May 16, 2021

22:41:11

May 16 2021 10:41:11:850PM

05-16-2021

2021/05/16

20210516

16 May 2021 22:41:11:850

22:41:11:850

2021-05-16 22:41:11

2021-05-16 22:41:11.850

2021-05-16T22:41:11.850

5 ???? 1442 10:41:11:850PM

5/10/1442 10:41:11:850PM

Oops Interview Question - 3

2021-05-16T15:57:00.010+05:30

52. What is the difference between a Hash Table and a Dictionary?

Hashtable	Dictionary
A Hashtable is a non-generic collection.	A Dictionary is a generic collection.
Hashtable is defined under System.Collections namespace.	Dictionary is defined under System.Collections.Generic namespace.
In Hashtable, you can store key/value pairs of the same type or of the different type.	In Dictionary, you can store key/value pairs of same type.
In Hashtable, there is no need to specify the type of the key and value.	In Dictionary, you must specify the type of key and value.
The data retrieval is slower than Dictionary due to boxing/ unboxing.	The data retrieval is faster than Hashtable due to no boxing/ unboxing.
In Hashtable, if you try to access a key that doesn’t present in the given Hashtable, then it will give null values.	In Dictionary, if you try to access a key that doesn’t present in the given Dictionary, then it will give error.
It is thread safe.	It is also thread safe but only for public static members.
It doesn’t maintain the order of stored values.	It always maintain the order of stored values.

Example Hash Table

using System;
using System.Collections;
  
class GFG {
  
    // Main method
    static public void Main()
    {
  
        // Create a hashtable
        // Using Hashtable class
        Hashtable my_hashtable = new Hashtable();
  
        // Adding key/value pair in the hashtable
        // Using Add() method
        my_hashtable.Add("A1", "Welcome");
        my_hashtable.Add("A2", "to");
        my_hashtable.Add("A3", "GeeksforGeeks");
  
        foreach(DictionaryEntry element in my_hashtable)
        {
            Console.WriteLine("Key:- {0} and Value:- {1} ",
                               element.Key, element.Value);
        }
    }
}

Output:
Key:- A3 and Value:- GeeksforGeeks 
Key:- A2 and Value:- to 
Key:- A1 and Value:- Welcome 

Example Dictionary

using System;

using System.Collections.Generic;

class GFG {

    // Main Method

    static public void Main()

{

        // Creating a dictionary

        // using Dictionary<TKey, TValue> class

        Dictionary<string, string> My_dict = 

                    new Dictionary<string, string>();

        // Adding key/value pairs in the Dictionary

        // Using Add() method

        My_dict.Add("a.01", "C");

        My_dict.Add("a.02", "C++");

        My_dict.Add("a.03", "C#");

        foreach(KeyValuePair<string, string> element in My_dict)

{

            Console.WriteLine("Key:- {0} and Value:- {1}", 

                              element.Key, element.Value);

}

}

}

Output:
Key:- a.01 and Value:- C
Key:- a.02 and Value:- C++
Key:- a.03 and Value:- C#

53. What are the state management techniques used in .Net?

HTTP Protocol is a Stateless protocol HTTP/HTTPs doesn't remember what website or URL we visited, or in other words we can say it doesn't hold the state of a previous website that we visited before closing our browser, that is called stateless. So how to maintain the state for request. This is called state management.

State Management Types

Client-side Management
Server-side Management

Client-side Techniques

Client-Side State Management, the state related information will directly get stored on the client-side. That specific information will travel back and communicate with every request generated by the user then afterwards provides responses after server-side communication.

View
Hidden
Cookies
Control State
Query Strings

Server-side Techniques

In Server-Side State Management all the information is stored in the user memory. Due to this functionality there is more secure domains at the server side in comparison to Client-Side State Management.

Session State
Application State

View State

It is page-level State Management
Used for holding data temporarily
Can store any type of data
Property dependent

Hidden Fields

Contains a small amount of memory
Direct functionality access

Cookies

Store information temporarily
It's just a simple small sized text file
Can be changed depending on requirements
User Preferred
Requires only a few bytes or KBs of space for creating cookies

Query String/Parameter

It is generally used for holding values
Works temporarily
Switches info from one to another page
Increase performance
Uses real and virtual path values for URL routing

Session State

The Session basically stores the values as a dictionary collection in key/value pairs. It completely utilizes server resources to store the data. It is a secure way of storing data, since the data will never be passed to the client.

For each and every user, a separate Session is created, and each and every Session has its Unique ID. This ID is being stored in the client's machine using cookies. If there are multiple users who are accessing a web application, then for each user a separate Session is created. If a single user logs in and logs out the Session is killed, then if the same user again logs into the application, then a new Session ID is being created for the same user.

The Session has a default timeout value (20 minutes). We can also set the timeout value for a session in the web.config file.

54. What is Data Abstraction?

Data abstraction is the process of hiding certain details and showing only essential information to the user. Abstraction can be achieved with either abstract classes or interfaces

The abstract keyword is used for classes and methods

55. What is Abstract Class?

Abstract class is a restricted class that cannot be used to create objects (cannot be instantiated).
To access it, it must be inherited from another class).
This class must contain at least one abstract method.
The Abstract classes are typically used to define a base class in the class hierarchy.
Abstract classes are either partially implemented or not implemented at all.
You can take advantage of abstract classes to design components and specify some level of common functionality that must be implemented by derived classes.
An abstract class can have both abstract and regular methods.

Example

abstract class Animal

{

public abstract void animalSound();

public void sleep()

{

Console.WriteLine("Zzz");

}

Animal myObj = new Animal(); // Will generate an error (Cannot create an instance of the abstract class or interface 'Animal')

56. What is Abstract Method?

Abstract method can only be used in an abstract class, and it does not have a body.
The body is provided by the derived class (inherited from).

57. What is Interface?

An interface is a completely "abstract class", which can only contain abstract methods and properties (with empty bodies)
By default, members of an interface are abstract and public.
Interfaces can contain properties and methods, but not fields.
Interface methods do not have a body - the body is provided by the "implement" class
On implementation of an interface, you must override all of its methods
An interface cannot contain a constructor (as it cannot be used to create objects)
An interface is a group of related methods with empty bodies.
C# does not support "multiple inheritance" (a class can only inherit from one base class). However, it can be achieved with interfaces, because the class can implement multiple interfaces.

Example

interface Animal

{

void animalSound(); // interface method (does not have a body)

void run(); // interface method (does not have a body)

}

58. What is the difference between Abstract class and Interface?

Abstract Class	Interface
It contains both declaration and definition part.	It contains only a declaration part.
Multiple inheritance is not achieved by abstract class.	Multiple inheritance is achieved by interface.
It contain constructor.	It does not contain constructor.
It can contain static members.	It does not contain static members.
Abstract class members can have access modifiers.	Interface members can’t have access modifiers.
Abstract class members can be private by default which can be change.	Interface members can be public by default which can not be change.
Abstract class can inherit from another abstract class or another interface.	Interface can inherit from another interface only and cannot inherit from an abstract class.
A class can only use one abstract class.	A class can use multiple interface.
If many implementations are of the same kind and use common behavior, then it is superior to use abstract class.	If many implementations only share methods, then it is superior to use Interface.
Abstract class can contain methods, fields, constants, etc.	Interface can only contain methods .
It can be fully, partially or not implemented.	It should be fully implemented.

How to create Abstract Classes and Interfaces?

public abstract class Customer

{

}

public interface ICustomer

{

}

How to create Abstract Classes and Interfaces along with fields?

public abstract class Customer

{

int i1;

}

public interface ICustomer

{

int i2;//Not possible

}

How to create Abstract Classes and Interfaces along with members?

public abstract class Customer

{

public abstract void Print1();

}

public interface ICustomer

{

void Print2();

}

How ismember implementation possible in Abstract Classes and Interfaces?

public abstract class Customer

{

public void Print1()

{

}

public interface ICustomer

{

void Print2()//Not possible

{

}

How to implement abstract or interface members in inherited class?

public abstract class Customer

{

public abstract void Print1();

}

public interface ICustomer

{

void Print2();

}

public class MainClass : Customer, ICustomer

{

public override void Print1()

{

}

public void Print2()

{

}

How to implement inherit from another Abstract Class or Interface to Abstract Class or Interface?

public abstract class Customer1

{

}

public abstract class Customer2 : Customer1

{

}

public abstract class Customer3 : Customer1, ICustomer1

{

}

public interface ICustomer1

{

}

public interface ICustomer2 : ICustomer1

{

}

public interface ICustomer3 : Customer1 //Not possible

{

}

Other Tech

2021-03-19T23:27:00.012+05:30

Docker

2021-03-19T21:04:00.020+05:30

Docker Basic Commands

docker -v --- Show Docker version
docker --version --- Show Docker version
docker or docker --help --- Show Docker all commands

docker pull image_name --- Pull an image or a repository from a registry
docker pull image_name:tab --- Pull an image or a repository from a registry
docker pull --all-tabs image_name:tab --- Pull an image or a repository from a registry with multiple images

docker start container_name--- Start one or more stopped containers
docker start -a container_name --- attached running container
docker start -i container_name --- Attach container's STDIN

docker run image_name --- Start a container from an image -- attached mode
docker run -d image_name --- run in back end (run in detached mode)
docker run image_name:tag --- tag is version by default docker pick latest version
docker run image_name sleep 5 --- sleep after 5 seconds
docker run --name Provide_new_name image_name --- Set container name
docker run -i image_name --- prompt interactive mode
docker run -it image_name --- prompt interactive mode in terminal
docker run -p 80:5000 image_name --- traffic on port 80 on docker host will get routed to port 5000 inside the docker contain
docker run -v /opt/datadir:/var/lib/mysql image_name --- /opt/datadir is the outside container where you want to save your container related data
docker run -e APP_COLOR=blue image_name --- set environment variable
docker run --network=none image_name --- run container on network none
docker run --network=host image_name --- run container on network host
docker run -v data_volume:/var/lib/mysql mysql --- mount volume
docker run -d -e MYSQL_ROOT_PASSWORD=db_pass123 --name mysql-db --network wp-mysql-network mysql:5.6 --- run container and adding network and environment variable

run = pull + start

CTRL + C stop running

docker exec container_name command [Arg...] --- Run a command in a running container

docker ps --- list running containers
docker ps -a --- list all containers (running or stopping)
docker ps -q --- list all containers id
docker ps | grep test --- list all containers and filter with name test
docker ps --last 1 --- Show n last created containers (includes all states)
docker ps --latest --- Show the latest created container (includes all states)
docker ps -s --- Display total file sizes

docker ps -f "status=exited" --- filtering flag with status
docker ps -a -f exited=1 --- filtering flag with status exited
docker ps -f id=39b7876aa786 --- filtering flag with id
docker ps -f name=nginx --- filtering flag with name

docker images --- list of running images
docker images -a --- list of all images
docker images --digests --- list of digests images
docker images --no-trunc --- list of digests images without truncate output
docker images -f "before=image_name" --- filter shows only images created before the image with given id or reference
docker images -f "since=image_name" --- filter shows only images created after the image with given id or reference
docker images -f "dangling=true" --- show un-tagged images
docker tag image_id new_image_name --- renaming the image name

docker stop container_name or container_id --- stop running container

docker rm container_name or container_id --- remove container
docker rmi container_name --- remove image
docker rmi $(docker images -f "dangling=true" -q) --- remove image using filter un-tagged images
docker port container_id --- check the port number for the container
docker kill container_name --- Force stop containers.
docker attach docker_container --- run in front end
docker logs container_name --- view specified container related logs
docker inspect container_name --- find details for specific container
docker build Dockerfile -t image_name --- build docker image
docker push image_name --- push docker image to repository/hub
docker history image_name --- Find the history of image
docker network ls --- list all networks
docker network inspect network_name --- inspect network details
docker network create --driver bridge --subnet 182.18.0.1/24 --gateway 182.18.0.1 image_name --- create network and adding driver, subnet and gateway
docker volume create data_volume --- create docker volume
docker service create --replicas=3 my-web-server --- create number of replicas

docker commit existing_container_id new_image_name --- Create a new image from a container’s changes
docker commit --change "ENV DEBUG=true" existing_container_name new_image_name --- new configuration
docker commit --change='CMD ["apachectl", "-DFOREGROUND"]' -c "EXPOSE 80" existing_container_name new_image_name --- commit container with cmd and expose instuction

docker service create --replicas=3 my-web-server --- create number of replicas
docker cp container: source_path destination_path --- Copy files/folders between a container and the local filesystem
dcoker create image_name --- Create a new container
docker diff container --- Inspect changes to files or directories on a container’s filesystem
docker export container --- Export a container’s filesystem as a tar archive

docker image ls --- list images
docker image pull --- Pull an image or a repository from a registry
docker image push --- Push an image or a repository to a registry
docker image inspect --- Display detailed information on one or more images
docker image history --- Show the history of an image
docker image build --- Build an image from a Dockerfile
docker image rm --- Remove one or more images
docker images --- List images

docker login --- Log in to a Docker registry
docker lgout --- Log out from Docker registry
docker logs container --- fetch the logs of a container
docker system df --- image container details summary
docekr stats --- docker stats

docker network connect network_name container_name --- Connect a container to a network
docker network disconnect network_name container_name --- Disconnect a container from a network
docker network create network_name --- Create a network
docker network inspect network_name --- Display detailed information on one or more networks
docker network ls -- list networks
docker network rm network_name --- Remove one or more networks

docker rename container_name new_Container_name --- Rename a container
docker restart container_name --- Restart one or more containers

Docker Commands Details

Commands:

attach Attach local standard input, output, and error streams to a running container

build Build an image from a Dockerfile

commit Create a new image from a container's changes

cp Copy files/folders between a container and the local filesystem

create Create a new container

diff Inspect changes to files or directories on a container's filesystem

events Get real time events from the server

exec Run a command in a running container

export Export a container's filesystem as a tar archive

history Show the history of an image

images List images

import Import the contents from a tarball to create a filesystem image

info Display system-wide information

inspect Return low-level information on Docker objects

kill Kill one or more running containers

load Load an image from a tar archive or STDIN

logout Log out from a Docker registry

logs Fetch the logs of a container

pause Pause all processes within one or more containers

port List port mappings or a specific mapping for the container

ps List containers

pull Pull an image or a repository from a registry

push Push an image or a repository to a registry

rename Rename a container

restart Restart one or more containers

rm Remove one or more containers

rmi Remove one or more images

run Run a command in a new container

save Save one or more images to a tar archive (streamed to STDOUT by default)

search Search the Docker Hub for images

start Start one or more stopped containers

stats Display a live stream of container(s) resource usage statistics

stop Stop one or more running containers

tag Create a tag TARGET_IMAGE that refers to SOURCE_IMAGE

top Display the running processes of a container

unpause Unpause all processes within one or more containers

update Update configuration of one or more containers

version Show the Docker version information

wait Block until one or more containers stop, then print their exit codes

Form a Docker Compose File From Docker Command

Below are the docker commands

docker run -d --name=redis redis

docker run -d --name=db postgres:9.4

docker run -d --name=vote -p 5000:80 --link redis:redis voting-app

docker run -d --name=result -p 5001:80 --link db:db result-app

docker run -d --name=worker --link db:db --link redis:redis worker

Note: link can be simply notify as

--link db:db

--link db

Compose Docker file from above commands

docker-compose.yml

------------------------------

version:

redis:

image: redis

db:

image: postgres:9.4

vote:

build: ./vote

port:

- 5000:80

links:

- redis

result:

build: ./result

ports:

- 5001:80

links:

- db

worker:

build: ./worker

links:

- redis

- db

Docker Compose Commands

docker compose create service_name --- Creates containers for a service.
docker compose convert one --format yaml --- Converts the compose file to platform’s yaml format
docker compose convert one --format json --- Converts the compose file to platform’s json format
docker compose down --- Stop and remove containers, networks
docker compose exec service_name command --- run command
docker compose kill service_name --- Force stop service containers.
docker compose ls --- List running compose projects
docker compose ps --- list containers
docker compose pull service_name --- pull service images
docker compose push service_name --- push service images
docker compose rm service_name --- Removes stopped service containers
docker compose run service_name --- Run a one-off command on a service.
docker compose start service_name --- Start services
docker compose stop service_name --- Stop services
docker compose top --- Display the running processes
docker compose up --- create and start containers

Docker-Compose Commands

docker-compose -v --- Docker version
docker-compose --version --- Docker version
docker-compose version --- Docker version

docker-compose config --- validate docker file

docker-compose ps --- displaying list of running docker-compose containers
docker-compose ps -a --- displaying lift of all docker compose containers
docker compose ps --- displaying lift of running docker compose containers
docker compose ps -a --- displaying lift of all docker compose containers

docker-compose ps == docker-compose ps -a == docker compose ps -a

docker-compose ps || grep=test --- filtering by container name
APP_PORT=80 docker-compose ps --- setting variable in compose file
docker-compose ps service_name ---- list out specific service

docker-compose build --- build container
docker-compose build service_name --- build specific service container

docker-compose up --- pulling and starting services containers from compose file
docker-compose -d up --- detached mode
docker-compose -f compose_file_yml up --- specifiying compose file name
docker-compose up --scale service_name=number_of_container ---adding scaling
APP_PORT=80 docker-compose up --- setting variable in compose file
docker-compose up -d service_name --- run specific service

docker-compose down --- stopping and removing services containers from compose file
docker-compose -f compose_file_yml down --- specifying compose file name
docker compose down service_name --- stop and remove specific service

docker-compose stop --- stop docker compose containers
docker-compose rm --- remove stopped docker compose containers

down = stop + rm

up = pull + start

docker-compose exec service_name command --- execute specific service and specific command

docker-compose log --- display all logs created by docker-compose
docker-compose log service_name --- display logs specific service created by docker-compose
docker-compose log -f service_name --- display logs specific service created by docker-compose

Dockerfile instruction arguments

FROM Sets the base image for subsequent

MAINTAINER Sets the author field of the generated images

RUN Execute commands in a new layer on top of the current image and commit the results

CMD Allowed only once (if many then last one takes effect)

LABEL Adds metadata to an image

EXPOSE Informs container runtime that the container listens on the specified network ports at runtime

ENV Sets an environment variable

ADD Copy new files, directories, or remote file URLs from into the filesystem of the container

COPY Copy new files or directories into the filesystem of the container

ENTRYPOINT Allows you to configure a container that will run as an executable

VOLUME Creates a mount point and marks it as holding externally mounted volumes from native host or other containers

USER Sets the username or UID to use when running the image

WORKDIR Sets the working directory for any RUN, CMD, ENTRYPOINT, COPY, and ADD commands

ARG Defines a variable that users can pass at build-time to the builder using --build-arg

ONBUILD Adds an instruction to be executed later, when the image is used as the base for another build

STOPSIGNAL Sets the system call signal that will be sent to the container to exit

Git Commands

2020-08-07T22:18:00.007+05:30

Basic

git --version
or
git -v

check git installed version

shortened

Config

git config user.name
git config user.email
git config --global user.name
git config --global user.email
git config user.name [UserName]
git config user.email [EmailId]
git config --global user.name [UserName]
git config --global user.email [EmailId]
git config --global --replace-all user.name Debashish

git config pull.rebase false
git config pull.rebase true
git config pull.ff only
git config --global alias.st status

git config --global pull.rebase false
git config --global pull.rebase true
git config --global pull.ff only

display configured user name
display configured user email
display globally configured user name
display globally configured user email
set user name in config
set user email in config
set user name globally in config
set user email globally in config
eliminate error during adding global username

merge (the default strategy)
Rebase
fast-forward only
configure st as alias for status

merge (the default strategy)
rebase
fast-forward only

Create a new repository

echo "# Git_V1" >> README.md
git init
git add README.md
git commit -m "first commit"
git branch -M master
git remote add origin [SSH Path for RemoteRepositoryURL]
git push -u origin master

Create and write a file README.md with content "# Git_V1"
initialize directory for git
add mark down file with name README
add commit message
rename the current branch to "master
add remote repository using URL
push changes to master

Push an existing repository from local to remote

git remote add origin [SSH Path for RemoteRepositoryURL]

git branch -M master

git push -u origin master

add remote repository using URL

rename the current branch to master

push your local master branch to a remote repository named origin and set it as the upstream branch

Clone a remote repository to local

git clone [SSH Path for RemoteRepositoryURL]

git clone –branch [BranchName] [RepositoryURL]

Clone a repository from remote to local machine

Clones a specific branch from a repository

Operations

git init

git init [Directory]

git add [FileName]

git add .

git remote add origin [SSH Path for Remote Repo]

git status

git diff

git diff --staged

git commit -m "[Message]"

git commit -a -m "[Message]"

git mv [FileName] [New_FileName]

git push -u origin master

git push -d origin [BranchName]

git pull origin master

initialize directory for git

create a new git repository in the specified directory

add given files to stage

add all unchanged files to stage

add repository to remote

show status of changes (tracked and untracked)

show difference between changes (modified vs unmodified)

show difference between changes between staged and unstaged

push changes to stage area

push changes

rename file

push changes to master

delete remote branch

update local repo from remote master repo

Undo/Delete

git rm [FileName]

git rm --cached [FileName]

git restore --staged [FileName]

git reset [FileName]

git reset

git revert [CommitId from above comman]

rm -rf .git

remove file and commit in stage

stop tracking file

changes back from stage area

addback given staged file to unstage

addback all staged files to unstage

create a new commit that undoes the changes made by a previous commit.

Delete .git file from repository

Branch

git branch
git branch [NewBranchName
git branch --merged
git branch --no-merged
git checkout [ExistingBranchName]
git checkout -b [NewBranchName]
git checkout --[FileName]
git checkout -f
git switch -c [NewBranchName]

git merge [BranchNameToMergeWithCurrentBranch]
git branch -d [BranchName]

list out all branch
create new branch
already merged branches
not merged branches
switch to existing mentioned branch
create new branch and switch to it
revert to previous stage for that file
revert to previous stage for all changes
create new branch and switch to it

Merge provided branch name to merge with current branch
Delete Branch

Stash

git stash -u
git stash list
git stash pop
git stash apply
git stash drop
git stash clear

temporarily save changes in your working directory, including untracked files
displays a list of all the stashed changes in your repository

apply the most recent stashed changes back to your working directory and then remove that stash from the stash list

reapply changes that you previously stashed with git stash

Drop the most recent stash

remove all stash entries from your stash list. This is a way to clean up your stash when you no longer need any of the stashed changes.

Log

git log
git log -p
git log -2
git log -p -2
git log --stat
git log --pretty=oneline
git log --pretty=short
git log --pretty=full
git log --pretty=format:"%h
git log --oneline

view the commit history of a Git repository in reverse chronological order (most recent first).
log with changed details
last two log
last two logs with changed details
show changed status
show changes in one line and in shorter view
show changes in short summary
show changes in full detail
log in pretty customized format (a-> author, e-> email)
show changes in one line

Log Pretty

git log --pretty=format:"%T -- %an"
git log --pretty=format:"%H -- %an"
git log --pretty=format:"%h -- %al"
git log --pretty=format:"%h -- %ad"
git log --pretty=format:"%h -- %ar"
git log --pretty=format:"%h -- %at"
git log --pretty=format:"%h -- %ai"
git log --pretty=format:"%h -- %aI"
git log --pretty=format:"%h -- %as"
git log --since=2.days
git log --since=2.weeks
git log --since=2.months
git log --author="[AuthorName]"
git log --before="Fri Aug 7 21:07:21 2020"

JSON VS CSON VS XML VS YAML

2020-05-19T22:11:00.000+05:30

JSON (JavaScript Object Notation)

{
"a": 1,
"b": [ 1, 2, 3 ],
"c": "Hello",
"d": true,
"e": "c"
}

CSON (CoffeeScript Object Notation)

"a": 1
"b":
-1
-2
-3
"c": "Hello"
"d": true
"e": "c"

XML (Extensible Markup Language)

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<root>
<a>1</a>
<b>1</b>
<b>2</b>
<b>3</b>
<c>Hello</c>
<d>true</d>
<e>c</e>
</root>

YAML (Human-Readable Data-Serialization Language)

a: 1
b:
- 1
- 2
- 3
c: "Hello"
d: true
e: 'c'

Autofac

2019-07-30T16:10:00.003+05:30

Example:

The basic pattern for integrating Autofac into your application is:

Structure your app with inversion of control (IoC) in mind.
Add Autofac references.
At application startup…
Create a ContainerBuilder.
Register components.
Build the container and store it for later use.
During application execution…
Create a lifetime scope from the container.
Use the lifetime scope to resolve instances of the components.

using Autofac;

using System;

namespace AutofacDemo

{

class Program

{

private static IContainer Container { get; set; }

static void Main(string[] args)

{

ContainerBuilder builder = new ContainerBuilder();

builder.RegisterType<Output>().As<IOutput>();

builder.RegisterType<DateWriter>().As<IDateWriter>();

//New Date Class Register With Date Interface

// Override Date Writer method with New Date Writer Method

builder.RegisterType<NewDateWriter>().As<IDateWriter>();

Container = builder.Build();

WriteDate();

Console.ReadLine();

}

private static void WriteDate()

{

using (var scope = Container.BeginLifetimeScope())

{

var writer = scope.Resolve<IDateWriter>();

writer.WriteDate();

}

public interface IOutput

{

void Write(string content);

}

public class Output : IOutput

{

public void Write(string content)

{

Console.WriteLine(content);

}

public interface IDateWriter

{

void WriteDate();

}

public class DateWriter : IDateWriter

{

private IOutput _output;

public DateWriter(IOutput output)

{

_output = output;

}

public void WriteDate()

{

_output.Write(DateTime.Today.ToShortDateString());

}

public class NewDateWriter : IDateWriter

{

private IOutput _output;

public NewDateWriter(IOutput output)

{

_output = output;

}

public void WriteDate()

{

_output.Write(DateTime.Today.AddDays(1).ToShortDateString());

}

Add Autofac Reference from Nuget

Please find code Repository here in GIT

Generics

2019-06-20T16:38:00.006+05:30

Generics allow us to design classes and methods decoupled from the data type.
Name Space: System.Collections.Generic

Example: Generic Method

using System;

namespace CSharpPracktice
{
public class Generics
{
public bool AreEqual<Type>(Type value1, Type value2)
{
return value1.Equals(value2);
}

}

public class GenericsCaller
{
public void Demo()
{
Generics generics = new Generics();
bool result = generics.AreEqual<string>("20", "20");

if (result)
Console.WriteLine("Equal");
else
Console.WriteLine("Not Equal");
}
}
}

Example: Generic Class

using System;

namespace CSharpPracktice
{
public class Generics<Type>
{
public bool AreEqual(Type value1, Type value2)
{
return value1.Equals(value2);
}

}

public class GenericsCaller
{
public void Demo()
{
Generics<string> generics = new Generics<string>();
bool result = generics.AreEqual("20", "20");

if (result)
Console.WriteLine("Equal");
else
Console.WriteLine("Not Equal");
}
}
}

Publish Subscriber Pattern

2019-06-14T11:49:00.002+05:30

Publish Subscriber Pattern (Observer Design Pattern)

The Publisher/Subscriber pattern is one of the variations of the Observer designer pattern
A publisher publishes a message and there are one or more Subscribers who capture the published message.
Publishers broadcast messages, with no knowledge of the subscribers.
Subscribers ‘listen’ out for messages regarding topic/categories that they are interested in without any knowledge of who the publishers are.
The event bus transfers the messages from the publishers to the subscribers.
Each subscriber only receives a subset of the messages that have been sent by the publisher, they only receive the message topics or categories they have subscribed to.

Event Bus knows what topic each subscriber is subscribed to. The event bus will filter messages based on topic and send the messages to subscribers that are subscribed to the topic of the message. The publishers are responsible for defining the topics of their messages.

To understand this consider a real-life scenario where Mobile operators are sending messages to their customers.

Callback

2019-06-13T16:45:00.002+05:30

Callback: (Opposite to synchronous process)

Function that will be called when a process is done executing a specific task.
Usage is usually in asynchronous logic.

Example in simple term

Synchronous Process:

Customer go to shopkeeper and order to customize a boot. Shopkeeper takes some time to customize it and rerun it back to the customer. Customer wait till the process and when customer get back the customized shoes it gifted to his neighbor. This complete process is the simple example of synchronous process as customer has to wait till the process of shoe customization not done by the shopkeeper.

Asynchronous Process (Callback):

Customer go to shopkeeper and order to customize a boot. Shopkeeper told to the customer that it will takes some time to customize it. Customer said that I do not want to wait for the process. Take your time and when process for customization will be done then please handover the shoes to my neighbor, I do not want to wait for the process to accomplished. Shopkeeper said OK sure. Customer go back. Shopkeeper customized the shoe which takes some time and once done shopkeeper handover the shoes to the neighbor. This process is the example of asynchronous process as customer do not have to wait till the process was executing and this is also example of callback as once process of customization has been done, shoes was handover to the neighbor by the shopkeeper, which was to be done by customer in the synchronized process.

Example:

public class CallbackDemo1
{
public delegate void DelegateSumOfNumbers(int x);

public void PrintSumOfNumbers(int num)
{
Console.WriteLine("Sum of numbers is " + num);
}

public void Demo()
{
int num = 5;

DelegateSumOfNumbers callBackSum = new DelegateSumOfNumbers(PrintSumOfNumbers);
InnerClassForSum innerClassForSum = new InnerClassForSum(num, callBackSum);

innerClassForSum.computeSum();
}

public class InnerClassForSum
{
private int number;
private DelegateSumOfNumbers _callBackSum;
public InnerClassForSum(int num, DelegateSumOfNumbers callBackSum)
{
number = num;
_callBackSum = callBackSum;
}
public void computeSum()
{
int sum = 0;
for (int i = 0; i <= number; i++)
{
sum += i;
}

_callBackSum(sum);
}
}
}

Delegate

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Prerequisite:

Type Safe: Can not move one data type to other data type. Type safety means preventing type errors. Type error happens when unknowingly developer assigns one data type to other causing bugs. In C# you can not assign one type value to another type value. C# is type safe, JavaScript is not type safe.
Conversion: Converts from one data type to other data type using the convert class.
Casting: Converts from one data type to other data type by defining the data type.
Implicit Casting: No need to define to cast from where to where. No data loss.
Explicit Casting: Need to define to cast from where to where. Data loss can happen.
Reference Type: Unlike value types, a reference type doesn't store its value directly. Instead, it stores the address where the value is being stored. In other words, a reference type contains a pointer to another memory location that holds the data.

Delegate:

Type safe function pointer.
Just like class and string, Delegate is also reference type.
Representative for the communication between two parties.
Real world use is to callback and do the data communication.

Example-1:

public class DelegateDemo
{

public delegate void DelegateName1();
public delegate int DelegateName2();
public delegate bool DelegateName3();
public delegate bool DelegateName4(int x);

public void method1()
{
Console.WriteLine("Method1 called.");
}

public int method2()
{
Console.WriteLine("Method2 called.");
return 0;
}

private bool method3()
{
Console.WriteLine("Method3 called.");
return false;
}

private bool method4(int x)
{
Console.WriteLine("Method4 called.");
return false;
}

public void method5()
{
Console.WriteLine("Method5 called.");
}

public void Demo()
{
// calling methods directly
method1();
method2();
method3();
method5();

// calling methods using reference i.e. delegate
Console.WriteLine("Calling from delegate");
DelegateName1 delegateName1 = new DelegateName1(method1);
delegateName1();
delegateName1.Invoke();

delegateName1 += method5;
delegateName1();

DelegateName2 delegateName2 = new DelegateName2(method2);
DelegateName3 delegateName3 = new DelegateName3(method3);
DelegateName4 delegateName4 = new DelegateName4(method4);

delegateName2();
delegateName3();
delegateName4(0);
}

}

Output:

Example-2:

Business Class

public class DelegateDemoBusinessClass
{
public delegate void DelGetCalculatedValue(int x, int y);

private int _x, _y;
private DelGetCalculatedValue _delegateObject;// = new DelGetCalculatedValue(getCalculatedValue);

public DelegateDemoBusinessClass(int x, int y, DelGetCalculatedValue getCalculatedValue)
{
_x = x;
_y = y;
_delegateObject = this.getCalculatedValue;
}
public void getCalculatedValue(int x, int y)
{
_delegateObject(x, y);
}
}

User (Caller) Class

public class DelegateDemoCallerClass
{
enum typeOperation { Addition = 0, Substraction = 1, Multiplication = 2, Division = 3 };
public static void Demo()
{
int x = 20, y = 10, operationChoice = 3;
DelegateDemoBusinessClass.DelGetCalculatedValue getCalculated;

if (operationChoice == Convert.ToInt32(typeOperation.Addition))
{
getCalculated = myAdd;
}
else if (operationChoice == Convert.ToInt32(typeOperation.Substraction))
{
getCalculated = mySub;
}
else if (operationChoice == Convert.ToInt32(typeOperation.Multiplication))
{
getCalculated = myMul;
}
else
{
getCalculated = myDiv;
}

DelegateDemoBusinessClass demobusinessclass = new DelegateDemoBusinessClass(x, y, getCalculated);

getCalculated(x, y);

}

public static void myAdd(int x, int y)
{
Console.WriteLine(x + y);
}
public static void mySub(int x, int y)
{
Console.WriteLine(x - y);
}
public static void myMul(int x, int y)
{
Console.WriteLine(x * y);
}
public static void myDiv(int x, int y)
{
Console.WriteLine(x / y);
}
}

Multicast Delegate:

That has references to more than one function.
Two approaches to create multicast delegate.
+ or += to register a method with the delegate
- or -= to un-register a method with the delete
Invokes the methods in the invocation list, the the same order in which they are added.
If the delegate has a return type other than void and if the delegate is a multicast delegate, only the value of the last invoked method will be returned.
If the delegate has an out parameter, the value of the output parameter, will be the value assigned by the last method.
Usage: Observer design pattern.

JavaScript

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Window Popup

alert("Hello! I am an alert box!")

Get Element By ID

document.getElementById('demo')// demo is the id of element
// Assign some value
document.getElementById('demo').innerHTML = Date();
document.getElementById('demo1').innerHTML = 'Magic'
// Change Font Size
document.getElementById('demo2').style.fontSize='35px'

Stop execution of debugging at certain point

debugger;

Hide

document.getElementById('demo1').style.display = 'none'

Display

document.getElementById('demo1').style.display = 'block'

Write in various form

document.write("This is document.write");
document.write("<br>");
document.write(10 * 5);
window.alert("This is window.alert");
console.log("this message is coming from console.log");

Function

//Accessing a function without () will return the function definition instead of the function result:

function toCelsius(fahrenheit) {
return (5/9) * (fahrenheit-32);
}
document.getElementById("demo").innerHTML = toCelsius;

Calling function

<input type="button" value="button1" onClick="myFunction()"/>
var text = "The temperature is " + toCelsius(77) + " Celsius";

Object

var car = {type:"Fiat", model:"500", color:"white"};

var person = {
firstName: "John",
lastName: "Doe",
age: 50,
eyeColor: "blue"
};

//The name:values pairs in JavaScript objects are called properties:

Accessing Object Properties

objectName.propertyName
//or
objectName["propertyName"]

Variable Declaration
// Simple string
var car = "Fiat"

The this Keyword

In a function definition, this refers to the "owner" of the function.
In other words, this.firstName means the firstName property of this object.

fullName : function() {
return this.firstName + " " + this.lastName;
}

<button onclick="this.innerHTML = Date()">The time is?</button>

//A method is a function stored as a property.

var person = {
firstName: "John",
lastName : "Doe",
id : 5566,
fullName : function() {
return this.firstName + " " + this.lastName;
}
};

String Operations

Length

txt.length;

Escape character

The backslash (\) escape character turns special characters into string characters
var x = "We are the so-called \"Vikings\" from the north.";

More
\b Backspace
\f Form Feed
\n New Line
\r Carriage Return
\t Horizontal Tabulator
\v Vertical Tabulator

Break Line string

var txt = "Hello \
Dolly!";

var txt = "Hello " +
"Dolly!";

var x = "John";
var y = new String("John");

// typeof x will return string
// typeof y will return object

Don't create strings as objects. It slows down execution speed.

String Index

str.indexOf("locate");
str.lastIndexOf("locate");

Both indexOf(), and lastIndexOf() return -1 if the text is not found.
Both methods accept a second parameter as the starting position for the search:

str.indexOf("locate", 15);

String Search

The search() method searches a string for a specified value and returns the position of the match:
str.search("locate");

The search() method cannot take a second start position argument.
The indexOf() method cannot take powerful search values (regular expressions).

String other operations

slice(start, end)
substring(start, end)
substr(start, length)
substring() is similar to slice().

The difference is that substring() cannot accept negative indexes.

<script>
var str = "Apple, Banana, Kiwi";
var res = str.slice(-12)
document.getElementById("demo").innerHTML = res;
</script>

output:
Banana, Kiwi

<script>
var str = "Apple, Banana, Kiwi";
var res = str.slice(7);
document.getElementById("demo").innerHTML = res;
</script>

output:
Banana, Kiwi

var x = 100 / "Apple";
isNaN(x);

Output:
true

-----

String Equal

When using the == operator, equal strings are equal:

When using the === operator, equal strings are not equal, because the === operator expects equality in both type and value.

var x = 500;
var y = new Number(500);
// (x == y) is true because x and y have equal values
// (x === y) is false because x and y have different types

toFixed()

returns a string, with the number written with a specified number of decimals:

var x = 9.656;
x.toFixed(0); // returns 10
x.toFixed(2); // returns 9.66
x.toFixed(4); // returns 9.6560
x.toFixed(6); // returns 9.656000

toPrecision()

returns a string, with a number written with a specified length:

var x = 9.656;
x.toPrecision(); // returns 9.656
x.toPrecision(2); // returns 9.7
x.toPrecision(4); // returns 9.656
x.toPrecision(6); // returns 9.65600

valueOf()

returns a number as a number.

var x = 123;
x.valueOf(); // returns 123 from variable x
(123).valueOf(); // returns 123 from literal 123
(100 + 23).valueOf(); // returns 123 from expression 100 + 23

Array

var cars = ["Saab", "Volvo", "BMW"];

var cars = [
"Saab",
"Volvo",
"BMW"
];

var cars = new Array("Saab", "Volvo", "BMW");

Array Vs Object

Arrays use numbers to access its "elements". In this example, person[0] returns John
var person = ["John", "Doe", 46];

Objects use names to access its "members". In this example, person.firstName returns John
var person = {firstName:"John", lastName:"Doe", age:46};

In JavaScript, arrays use numbered indexes.
In JavaScript, objects use named indexes.

var fruits = ["Banana", "Orange", "Apple", "Mango"];
fruits.length; // the length of fruits is 4

fruits = ["Banana", "Orange", "Apple", "Mango"];
var first = fruits[0];//Accessing the First Array Element
var last = fruits[fruits.length - 1];//Accessing the Last Array Element

Looping Array Elements

var fruits, text, fLen, i;
fruits = ["Banana", "Orange", "Apple", "Mango"];
fLen = fruits.length;

text = "<ul>";
for (i = 0; i < fLen; i++) {
text += "<li>" + fruits[i] + "</li>";
}
text += "</ul>";

var fruits, text;
fruits = ["Banana", "Orange", "Apple", "Mango"];

text = "<ul>";
fruits.forEach(myFunction);
text += "</ul>";

function myFunction(value) {
text += "<li>" + value + "</li>";
}

var fruits = ["Banana", "Orange", "Apple", "Mango"];
fruits.push("Lemon"); // adds a new element (Lemon) to fruits

JavaScript does not support arrays with named indexes.
In JavaScript, arrays always use numbered indexes.

----

var fruits = ["Banana", "Orange", "Apple", "Mango"];
document.getElementById("demo").innerHTML = fruits.toString();
document.getElementById("demo1").innerHTML = fruits.join(" * ");

output:
Banana,Orange,Apple,Mango
Banana * Orange * Apple * Mango

The pop, push, shift, unshift

method removes the last element from an array:
var fruits = ["Banana", "Orange", "Apple", "Mango"];
fruits.pop(); // Removes the last element ("Mango") from fruits

var fruits = ["Banana", "Orange", "Apple", "Mango"];
var x = fruits.pop(); // the value of x is "Mango"

var fruits = ["Banana", "Orange", "Apple", "Mango"];
fruits.push("Kiwi"); // Adds a new element ("Kiwi") to fruits

var fruits = ["Banana", "Orange", "Apple", "Mango"];
var x = fruits.push("Kiwi"); // the value of x is 5

The shift() method removes the first array element and "shifts" all other elements to a lower index.
var fruits = ["Banana", "Orange", "Apple", "Mango"];
fruits.shift(); // Removes the first element "Banana" from fruits

var fruits = ["Banana", "Orange", "Apple", "Mango"];
var x = fruits.shift(); // the value of x is "Banana"

The unshift() method adds a new element to an array (at the beginning), and "unshifts" older elements:

var fruits = ["Banana", "Orange", "Apple", "Mango"];
fruits.unshift("Lemon"); // Adds a new element "Lemon" to fruits

var fruits = ["Banana", "Orange", "Apple", "Mango"];
fruits.unshift("Lemon"); // Returns 5

----

The length property provides an easy way to append a new element to an array:

var fruits = ["Banana", "Orange", "Apple", "Mango"];
fruits[fruits.length] = "Kiwi"; // Appends "Kiwi" to fruits

Since JavaScript arrays are objects, elements can be deleted by using the JavaScript operator delete:

var fruits = ["Banana", "Orange", "Apple", "Mango"];
delete fruits[0]; // Changes the first element in fruits to undefined

Using delete may leave undefined holes in the array. Use pop() or shift() instead.

The splice()

method can be used to add new items to an array:

var fruits = ["Banana", "Orange", "Apple", "Mango"];
fruits.splice(2, 0, "Lemon", "Kiwi");

The first parameter (2) defines the position where new elements should be added (spliced in).
The second parameter (0) defines how many elements should be removed.
The rest of the parameters ("Lemon" , "Kiwi") define the new elements to be added.
The splice() method returns an array with the deleted items:

String concat

var myGirls = ["Cecilie", "Lone"];
var myBoys = ["Emil", "Tobias", "Linus"];
var myChildren = myGirls.concat(myBoys); // Concatenates (joins) myGirls and myBoys

var arr1 = ["Cecilie", "Lone"];
var arr2 = ["Emil", "Tobias", "Linus"];
var arr3 = ["Robin", "Morgan"];
var myChildren = arr1.concat(arr2, arr3); // Concatenates arr1 with arr2 and arr3

var arr1 = ["Cecilie", "Lone"];
var myChildren = arr1.concat(["Emil", "Tobias", "Linus"]);

The slice, sort, referese()

method slices out a piece of an array into a new array.
This example slices out a part of an array starting from array element 1 ("Orange"):

var fruits = ["Banana", "Orange", "Lemon", "Apple", "Mango"];
var citrus = fruits.slice(1);

var fruits = ["Banana", "Orange", "Apple", "Mango"];
fruits.sort(); // First sort the elements of fruits
fruits.reverse(); // Then reverse the order of the elements

var points = [40, 100, 1, 5, 25, 10];

points.sort(function(a, b){return a - b}); //Ascending
points.sort(function(a, b){return a - b}); //Descending

Static

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Static keyword has different role in different places for C#. When we declare static that means only single copy will be generate.

Static container can only contains static members

It is used in below places-

Class
Method
Field
Properties
Constructor

Static Class

Only contain all static members like static methods, static fields, static properties and static constructor.
Any instance or non-static member can not be there in the Static Class.
If we need to create all the members as static then we can create static class.
Can not create instance of such class.
Sealed.
Cannot contain Instance Constructors

Static Methods

Only contain all static fields
Non-static fields are not allowed in static methods
Method can be access using class only, no instance is needed or can access.
Single copy of static method will be shared among all the instances.

Static Fields

Single copy of fields/variables get created and shared among all the instances.
If static variable value has been change using one instance then all other instance will get that changed value.

Static Property

Can be access using class only.
Using instance it can not be access.

Static Constructor

Access modifier are not allowed.
Static Constructor as it(class constructor) execute prior to any other constructor (instance constructor).
Can instantiate value of static fields only.
Non-Static fields is not allowed within the scope.

More About Static:

Static methods are not allowed in the interface.
Access modifiers are not allowed in the interface and static constructor.
Static class can't be inherit from interface/class/static class.
Static class can only be inherit from object. ??
Inheritance from static class in not possible as static classes are sealed.
Inherited Static method can not be marked as override, virtual or abstract.
Inherited Static methods can be marked as new.

Structured/Imperative/Functional/Procedural Programming

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Structured Programming

Top-down analysis

Problem broken down into small piece (sub-problems) where each one has some significance.
Each small piece of problems are individually solved and steps are clearly stated.

Modular Programming

Code is broke down into small groups of instructions
These groups are knows as modules or subprograms or subroutines or methods.
Avoid jumps (unconditional GoTo) as non-traceable

Structured Code

Divide modules into further small units of code

Follow Top Down design model
Maintainable Code
Systematic Organization
Reusable code block
Subdivision of program into functions
Hierarchy of task
Simple and easy to understand the code
Avoid unconditional Goto

Un-Structured code

Unconditional Goto

Imperative languages

Imperative programming is a paradigm of computer programming in which the program describes a sequence of steps that change the state of the computer.
Unlike declarative programming, which describes "what" a program should accomplish, imperative programming explicitly tells the computer "how" to accomplish it.
To make programs simpler for a human to read and write, imperative statements can be grouped into sections known as code blocks.

Functional Programming

Functional programming (FP) is about passing data from function to function to get a result.
In FP, functions are treated as data, meaning you can use them as parameters, return them, build functions from other functions, and build custom functions.
A functional approach involves composing the problem as a set of functions to be executed.
In software, everything is a statement, unless it is a function.

Procedural Programming

Procedural programming is a programming paradigm, derived from structured programming
Based upon the concept of the procedure call. Procedures
Also known as routines, subroutines, or functions, simply contain a series of computational steps to be carried out.
Any given procedure might be called at any point during a program's execution, including by other procedures or itself.
Procedural programming (PP), also known as inline programming takes a top-down approach.
It is about writing a list of instructions to tell the computer what to do step by step.
It relies on procedures or routines.
Procedural programming is a type of imperative programming in which the program is built from one or more procedures (also termed subroutines or functions).
Procedural programming could be considered a step towards declarative programming.
A programmer can often tell, simply by looking at the names, arguments, and return types of procedures (and related comments), what a particular procedure is supposed to do, without necessarily looking at the details of how it achieves its result.
At the same time, a complete program is still imperative since it fixes the statements to be executed and their order of execution to a large extent.

Singleton Pattern

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Singleton Pattern belongs to Creational type pattern. As the name implies, creational design type deals with object creation mechanisms. Basically, to simplify this, creational pattern explains us the creation of objects in a manner suitable to a given situation.

Singleton design pattern is used when we need to ensure that only one object of a particular class is Instantiated. That single instance created is responsible to coordinate actions across the application.

If you look at the illustrated diagram above, you will see different objects trying to invoke an object instantiated as singleton. This single instance of the object is responsible to invoke underneath methods or events.

Advantages and Guidelines for Singleton implementation.

Concurrent access to the resource is well managed by singleton design pattern.

As part of the Implementation guidelines we need to ensure that only one instance of the class exists by declaring all constructors of the class to be private. Also, to control the singleton access we need to provide a static property that returns a single instance of the object.

Singleton Class Implementation Example

Program.cs

namespace SingletonDemo

{

class Program

{

static void Main(string[] args)

{

* Assuming Singleton is created from employee class

* we refer to the GetInstance property from the Singleton class

Singleton fromEmployee = Singleton.GetInstance;

fromEmployee.PrintDetails("From Employee");

* Assuming Singleton is created from student class

* we refer to the GetInstance property from the Singleton class

Singleton fromStudent = Singleton.GetInstance;

fromStudent.PrintDetails("From Student");

Console.ReadLine();

}

Singleton.cs

namespace SingletonDemo

{

* Sealed ensures the class being inherited and

* object instantiation is restricted in the derived class

public sealed class Singleton

{

private static int counter = 0;

* Private property initilized with null

* ensures that only one instance of the object is created

* based on the null condition

private static Singleton instance = null;

* public property is used to return only one instance of the class

* leveraging on the private property

public static Singleton GetInstance

{

get

{

if (instance == null)

instance = new Singleton();

return instance;

}

* Private constructor ensures that object is not

* instantiated other than with in the class itself

private Singleton()

{

counter++;

Console.WriteLine("Counter Value " + counter.ToString());

}

* Public method which can be invoked through the singleton instance

public void PrintDetails(string message)

{

Console.WriteLine(message);

}

Lazy Initialization in Singleton : GetInstance Property is responsible for the Singleton Instance creation. Singleton object is not instantiated until and unless GetInstance is invoked. Hence, there is a delay in instance creation till the GetInstance is accessed. This Delay in Instance creation is called Lazy Initialization.

How to use Multithreads in Singleton : The lazy initialization works perfectly well when we invoke the GetInstance in a Single threaded approach. However, there is a chance that we may end up creating multiple instances when multiple threads invoke the GetInstance at the same time.

This Thread racing situation causes thread safety issues in Singleton Initialization and further the current code ends up in creating multiple instances of Singleton objects in memory.

To achieve and replicate multiple threads accessing GetInstance, We have modified the main program by using Parallel.Invoke method of .NET Framework 4.0. Please refer to Main program code below for more details.

How to implement a Thread Safe singleton class : Locks are the best way to control thread race condition and they help us to overcome the present situation. Please refer to the Singleton.cs code for lock checks and double check locking.

static void Main(string[] args)

{

Parallel.Invoke(

() => PrintStudentdetails(),

() => PrintEmployeeDetails()

);

Console.ReadLine();

}

private static readonly object obj = new object();

public static Singleton GetInstance

{

get

{

if (instance == null)

{

lock (obj)

{

if (instance == null)

instance = new Singleton();

}

return instance;

}

Difference between Lazy Initialization and Eager Initialization

Lazy Initialization:

The lazy initialization of an object improves the performance and avoids unnecessary computation till the point the object is accessed. Further, it reduces the memory footprint during the start-up of the program. Reducing the memory print will help faster loading of the application.

Non-Lazy or Eager Loading:

Eager loading is nothing but to initialize the required object before it’s being accessed. Which means, we instantiate the object and keep it ready and use it when we need it. This type of initialization is used in lower memory footprints. Also, in eager loading, the common language runtime takes care of the variable initialization and its thread safety. Hence, we don’t need to write any explicit coding for thread safety.

Singleton with Lazy keyword (.NET 4.0):

Lazy keyword provides support for lazy initialization. In order to make a property as lazy, we need to pass the type of object to the lazy keyword which is being lazily initialized.

By default, Lazy<T> objects are thread-safe. In multi-threaded scenarios, the first thread which tries to access the Value property of the lazy object will take care of thread safety when multiple threads are trying to access the Get Instance at the same time.

Therefore, it does not matter which thread initializes the object or if there are any thread race conditions that are trying to access this property.

private static readonly Lazy<Singleton> instance =

new Lazy<Singleton>(()=>new Singleton());

Differences between Singleton and static classes

1. Static is a keyword and Singleton is a design pattern

2. Static classes can contain only static members

3. Singleton is an object creational pattern with one instance of the class

4. Singleton can implement interfaces, inherit from other classes and it aligns with the OOPS concepts

5. Singleton object can be passed as a reference

6. Singleton supports object disposal

7. Singleton object is stored on heap

8. Singleton objects can be cloned

Real world usage of Singleton:

Listed are few real world scenarios for singleton usage

1. Exception/Information logging

2. Connection pool management

3. File management

4. Device management such as printer spooling

5. Application Configuration management

6. Cache management

7. And Session based shopping cart are some of the real world usage of singleton design pattern

Additional Examples

Real World Example

Design Patterns

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Design patterns are reusable solutions to the problems that we encounter in the day to day programming. They are generally targeted at solving the problems of object generation and integration. In other words, Design patterns acts as templates which can be applied to the real-world programming problems.

Design patterns are solutions to software design problems you find again and again in real-world application development. Patterns are about reusable designs and interactions of objects.

Types of Design Patterns

Gang of Four have categorised the design patterns in to 3 types based on different problems encountered in the real world applications. They are Creational, Structural and Behavioural.

Creational design patterns :

These patterns deal with object creation and initialization. Creational pattern gives the program more flexibility in deciding which objects need to be created for a given case.

Examples: Singleton , Factory and Abstract Factory etc.

Structural design patterns :

This pattern deals with class and object composition. In simple words, This pattern focuses on decoupling interface, implementation of classes and its objects.

Examples: Adapter, Facade and Bridge etc.

Behavioural design patterns :

These patterns deal with communication between Classes and objects.

Examples: Chain of Responsibility, Command and Interpreter etc.

Design Pattern Sample with Real world examples

Class & Object

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Class:

Blue Print (set of instruction to build a specific type of object) or prototype that defines the variables and the methods (functions) common to all objects of a certain kind.
Class is just logical representation.
Not stored in any memory.

Object

Instance of class.
Physical representation of the class.
Block of memory that has been allocated.
Stored in memory (i.e variables present in class).
Helps us to access the member of a class or struct either they can be fields, methods or properties
A program may create many objects of the same class.
Consists of methods and properties to make a particular type of data useful

Class Vs Object

Class is a template from which objects are created.
Object determines the behavior of the class.
Class is an entity that determines how an object will behave and what the object will contain.

Wrapper Class

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If we want to hide some set of logic (written in some class) and/or attributes from outside the world then instead of adding access modifier (private specially), we can move all those logic and attributes to some place (class, which encapsulate attributes and actions) and wrap that class within the another class. So by this way we can hide the whole logic from outside the class as by creating the object of the wrapper class we cannot access the method inside the wrapped class.

E.G.

public class WrapperClass

{

public int AddNumber(int a, int b)

{

return a + b;

}

public void AddNumberW(int a, int b)

{

WrappedClass wc = new WrappedClass();

Console.WriteLine("Adding specific values using default constrctor= " + wc.AddNumberW(3,5));

}

public class WrappedClass

{

public int AddNumberW(int a, int b)

{

return a + b;

}

Managed Heap

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Address spaces, created by processes at run time.

Work based on automatic memory management.

Microsoft’s .NET framework uses a managed heap model as part of its automatic memory management process.

When you create an object using the new operator in C#, the .NET run time allocates memory in the "managed heap" (simply a heap managed by the .NET run time + the garbage collector).

Automatic memory management is one of the services that the Common Language Run time provides during Managed Execution.

The Common Language Run time's garbage collector manages the allocation and release of memory for an application. For developers, this means that you do not have to write code to perform memory management tasks when you develop managed applications. Automatic memory management can eliminate common problems, such as forgetting to free an object and causing a memory leak, or attempting to access memory for an object that has already been freed.

When you initialize a new process, the run time reserves a contiguous region of address space for the process. This reserved address space is called the managed heap. The managed heap maintains a pointer to the address where the next object in the heap will be allocated. Initially, this pointer is set to the managed heap's base address. All reference types are allocated on the managed heap. When an application creates the first reference type, memory is allocated for the type at the base address of the managed heap. When the application creates the next object, the garbage collector allocates memory for it in the address space immediately following the first object. As long as address space is available, the garbage collector continues to allocate space for new objects in this manner.

Allocating memory from the managed heap is faster than unmanaged memory allocation. Because the run time allocates memory for an object by adding a value to a pointer, it is almost as fast as allocating memory from the stack. In addition, because new objects that are allocated consecutively are stored contiguously in the managed heap, an application can access the objects very quickly.

The garbage collector's optimizing engine determines the best time to perform a collection based on the allocations being made. When the garbage collector performs a collection, it releases the memory for objects that are no longer being used by the application. It determines which objects are no longer being used by examining the application's roots. Every application has a set of roots. Each root either refers to an object on the managed heap or is set to null. An application's roots include static fields, local variables and parameters on a thread's stack, and CPU registers.

Objects that are not in the graph are unreachable from the application's roots. The garbage collector considers unreachable objects garbage and will release the memory allocated for them. During a collection, the garbage collector examines the managed heap, looking for the blocks of address space occupied by unreachable objects. As it discovers each unreachable object, it uses a memory-copying function to compact the reachable objects in memory, freeing up the blocks of address spaces allocated to unreachable objects. Once the memory for the reachable objects has been compacted, the garbage collector makes the necessary pointer corrections so that the application's roots point to the objects in their new locations. It also positions the managed heap's pointer after the last reachable object. Note that memory is compacted only if a collection discovers a significant number of unreachable objects. If all the objects in the managed heap survive a collection, then there is no need for memory compaction.

To improve performance, the run time allocates memory for large objects in a separate heap. The garbage collector automatically releases the memory for large objects. However, to avoid moving large objects in memory, this memory is not compacted.

Struct

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Struct is an encapsulated entity. Struct doesn't uses complete oops concept but are used for user defined data type. All the member of the struct has to be initialized, as it is value type.
A struct is a simple user-defined type, a lightweight alternative to a class.
Similar to classes, structures have behaviors and attributes. As a value type, structures directly contain their value so their object or instance is stored on the stack.
Struts support access modifiers, constructors, indexers, methods, fields, nested types, operators, and properties.
Whenever you have a need for a type that will be used often and is mostly just a piece of data, structs might be a good option. In the other words when we have small and frequent use of some work use structs over classes.
Structs reside on the stack, so we should keep them small.
The default constructor of a structure initializes each field to a default value. You cannot replace the default constructor of a structure.
You can't define destructor for structs

E.G.

public struct Student {

int id;

int zipcode;

double salary;

}

Q: Is Structure reference type?

A: No, it is value type

Q: Is Structure support default (parameter less) constructor?

A: No

Q: Is Structure support parameterized constructor?

A: Yes

Q: Is Structure support uninitialized valued (attributes)?

A: No, all values must be initialized within constructor. We cannot initialize value during declaration.

Q: Can Structure be inherited?

A: No, they are sealed.

Q: Can class be inheriting to Structure?

A: No. Struct can't derive from any class.

Q: Can Interface be inheriting to Structure?

A: Yes. Struct can be derive from interface only.

Q: Can Structure member be declared protected?

A: No, as Structure cannot inherited.

Structure VS Class

Structs	Class
Value Type	Reference Type
Stored in stack	Stored on managed heap
Doesn’t support inheritance with class	Support Inheritance
Cannot define default constructor	Constructor is fully supported
Cannot define default destructor	Destructor is fully supported
Uninitialized member not possible	Uninitialized member possible

Object Relational Mapping (ORM)

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(ORM) is a technique that lets you query and manipulate data from a database using an object-oriented paradigm

An ORM library is a completely ordinary library written in your language of choice that encapsulates the code needed to manipulate the data, so you don't use SQL anymore; you interact directly with an object in the same language you're using

E.G.

book_list = new List();

sql = "SELECT book FROM library WHERE author = 'Linus'";

data = query(sql); // I over simplify ...

while (row = data.next())

{

book = new Book();

book.setAuthor(row.get('author');

book_list.add(book);

}

With an ORM library, it would look like this:

book_list = BookTable.query(author="Linus");

Disadvantage of ORM

· ORM libraries are not lightweight tools;

· Performance is OK for usual queries, but a SQL master will always do better with his own SQL for big projects.

Example of ORM

Entity Framework

SQL Theory Interview Questions

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1. Advantages and Disadvantages of Stored Procedure

Stored procedure can be used as a modular programming – means create once, store and call for several times whenever required.

This supports faster execution instead of executing multiple queries. This reduces network traffic and provides better security to the data.

Disadvantage is that it can be executed only in the Database and utilizes more memory in the database server.

2. What are different SQL statement

There are 3 types of SQL statements

1) DDL (Data Definition Language): It is used to define the database structure such as tables. It includes three statements such as Create, Alter, and Drop.

Some of the DDL Commands are listed below

CREATE: It is used for creating the table.

CREATE TABLE&amp;amp;nbsp;table_name

column_name1 data_type(size),

column_name2 data_type(size),

column_name3 data_type(size),

ALTER: The ALTER table is used for modifying the existing table object in the database.

ALTER TABLE table_name

ADD column_name datatype

ALTER TABLE table_name

DROP COLUMN column_name

2) DML (Data Manipulation Language): These statements are used to manipulate the data in records. Commonly used DML statements are Insert, Update, and Delete.

The Select statement is used as partial DML statement that is used to select all or relevant records in the table.

3) DCL (Data Control Language): These statements are used to set privileges such as Grant and Revoke database access permission to the specific user.

What are different JOINS used in SQL?

· Right Join

· Outer Join

· Full Join

· Cross Join

· Self Join

3. What is SQL Injection?

SQL Injection is a type of database attack technique where malicious SQL statements are inserted into an entry field of database such that once it is executed the database is opened for an attacker. This technique is usually used for attacking Data-Driven Applications to have an access to sensitive data and perform administrative tasks on databases.

4. What is the difference between DELETE and TRUNCATE?

The basic difference in both is DELETE is DML command and TRUNCATE is DDL

DELETE is used to delete a specific row from the table whereas TRUNCATE is used to remove all rows from the table

We can use DELETE with WHERE clause but cannot use TRUNCATE with it

5. What is the difference between DROP and TRUNCATE?

TRUNCATE removes all rows from the table which cannot be retrieved back, DROP removes the entire table from the database and it cannot be retrieved back.

6. What is Trigger?

Ans. Trigger allows us to execute a batch of SQL code when a table event occurs (Insert, update or delete command executed against a specific table)

A SQL trigger is a special type of stored procedure. It is special because it is not called directly like a stored procedure. The main difference between a trigger and a stored procedure is that a trigger is called automatically when a data modification event is made against a table whereas a stored procedure must be called explicitly.

7. Advantages of using SQL triggers

SQL triggers provide an alternative way to check the integrity of data.

SQL triggers provide an alternative way to run scheduled tasks. By using SQL triggers, you don’t have to wait to run the scheduled tasks because the triggers are invoked automatically before or after a change is made to the data in the tables.

SQL triggers are very useful to audit the changes of data in tables.

Types of Trigger

DDL Triggers

In SQL Server we can create triggers on DDL statements (like CREATE, ALTER, and DROP) and certain system defined stored procedures that perform DDL-like operations.

DML Triggers

In SQL Server we can create triggers on DML statements (like INSERT, UPDATE, and DELETE) and stored procedures that perform DML-like operations. DML Triggers are of two types

After Trigger (using FOR/AFTER CLAUSE)

This type of trigger fires after SQL Server finish the execution of the action successfully that fired it.

Instead of Trigger (using INSTEAD OF CLAUSE)

This type of trigger fires before SQL Server starts the execution of the action that fired it. This is differ from the AFTER trigger, which fires after the action that caused it to fire. We can have an INSTEAD OF insert/update/delete trigger on a table that successfully executed but does not include the actual insert/update/delete to the table.

8. What are the properties of a transaction?

ACID (an acronym for Atomicity, Consistency Isolation, Durability) is a concept that Database Professionals generally look for when evaluating databases and application architectures. For a reliable database all these four attributes should be achieved.

Atomicity is an all-or-none proposition.

Consistency guarantees that a transaction never leaves your database in a half-finished state.

Isolation keeps transactions separated from each other until they’re finished.

Durability guarantees that the database will keep track of pending changes in such a way that the server can recover from an abnormal termination.

SQL

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