Saturday, August 2, 2014

OOPs Concept Example

Abstract and Virtual:
•If a class is to serve the purpose of providing common fields and members to all subclasses, we create an Abstract class. For creating an abstract class, we make use of the abstract keyword. Such a class cannot be instantiated.
•Whatever functionality in common to the entire system which functionality put together and keep into separate.


Why do we need Abstract class:

•Take three classes Human, Man and Woman. All Man and Woman belong to Human category. In Original object exists for only for Man or Woman. NO object exists for Human category. But both Man and Woman have common characteristics where we can say it as Human characters. Now you can understand that why do we need abstract class.


Abstract Rules
-> We cannot create object for abstract class
-> we cannot declare the abstract method in non abstract class
-> we cannot declare the non abstract method or virtual method without declare the body
-> We cannot declare a body in abstract method
-> When at least one of the methods in the class is abstract.
-> Abstract can extend only one abstract class.
->An abstract class can extend c# class only
Difference between Abstract and Virtual

Abstract
Virtual
No Keyword
Can have implementation? 
No
Yes
Yes
Can override?
Must
Can but not a must
You can declare a new method with the same name
Which keyword to use to provide new implementation in the   concrete class?
override
override
No keyword needed
If an object is created of thebase class type, which method will be executed?
Concrete implementation
The parent implementation will be called only if no implementation is provided in the concrete class
Parent implementation
If an object is created of the concrete class type, which method will be executed?
Concrete implementation
Concrete implementation
The parent implementation will be called only if no implementation is provided in the concrete class


Interface  
     
•Interface nothing but skeleton of the class   
•We cant create object for interface     
•It s a Pure abstraction     
•Pure abstraction means you cannot have concrete methods   
•Interfaces should not have any concrete methods, it should only have method declarations.     
A method with definition is concrete method    
     
     
In which scenario we use Interfaces:     
     
•If your child classes should all implement a certain group of methods/functionalities but each of the child classes is free to provide its own implementation then use interfaces. 
•For e.g. if you are implementing a class hierarchy for vehicles implement an interface called Vehicle which has properties like Color MaxSpeed etc. and methods like Drive(). All child classes like Car Scooter Airplane Solar Car etc. should derive from this base interface but provide a separate implementation of the methods and properties exposed by Vehicle   
Which one is advantage over another:     
     
•Interface has advantage over Abstract class. Since you can not use abstract class for already inherited class. But you can use interface for already inherited class.    
     
     
     
Difference between Abstract and Interface:     

Interface
Abstract
1.A class can implement multiple interface
1.Abstract can extend only one abstract class.
●
●
2.An interface can extend another interface
2.An abstract class can extend c# class only
●
●
3.Interface contain only method and propertied . (can t declare variables)
3.It contains private member also we can put some methods with implementation.
●
●
4.EX:
4.Ex:
Public interface
Public abstract class vehicles
{
{
 Void accelerator();
 Private intnoofwheels;
String engine{
 Private string color;
Get;
 Public abstract string engine
Set;
 {
}
 Get;
}
 Set;
5.I can say that interface is for "PURE ABSTRACTION". Pure abstraction means  you can not have concrete methods. A method with definition is Concrete method.
 }
●
Public abstract void accelerator();
}
5.   But abstract class can have concrete methods.
Implementing few methods of a interface class-C#     
     
•We declared 10 methods in interface, now we should implement all 10 methods. But we want implement 2 methods only.    
•How?
•Example.  
     
Sealed Class:    
     
•Sealed classes are used to restrict the inheritance feature of object oriented programming     
•A sealed class cannot be used as a base class.
•Sealing a class means one cannot derive from it.    
•A method means one cannot override it.  
•Example.  
Polymorphism     
•Polymorphism means many forms.    
•Polymorphism is the ability to process objects differently depending on their data types.     
•Polymorphism is the ability to redefine methods for derived classes.  
     
Polymorphism provides following features:      
•It allows you to invoke methods of derived class through base class reference during runtime.   
•It has the ability for classes to provide different implementations of methods that are called through the same name.
     
Polymorphism     
     
Polymorphism is of two types:      
1.Compile time polymorphism/Overloading  
2.Runtime polymorphism/Overriding  
Compile Time Polymorphism    
• Compile time polymorphism is method overloading. It is also called early binding.
• In method overloading method performs the different task at the different input parameters.     
Runtime Time Polymorphism    
• Runtime time polymorphism is done using inheritance and virtual functions. Method overriding is called runtime polymorphism. It is also called late binding    
     
Overloading:     
•Overloading a method simply involves having another method with the same prototype.     
Overriding 
•To change the behavior of the method for the derived class
Note 
•Method overloading has nothing to do with inheritance or virtual methods.   
Following are examples of methods having different overloads:    
•void area(int side);  
•void area(int l, int b);    
•Void area(int l, double b, int c) 
•Void area(double b, int l, int c) 
•void area(float radius);    
Polymorphism     
     
When and why to use method overloading   
     
• Use method overloading in situation where you want a class to be able to do something, but there is more than one possibility for what information is supplied to the method that carries out the task.  
     
• You should consider overloading a method when you for some reason need a couple of methods that take different parameters, but conceptually do the same thing.    
•Example   
•    
• Void Area(int a)  //Square 
•Void Area(int h,int w)  //Rectangle     
•Void Area(int a, int l, int w)  //Cylinder    
•Void Area(int  pi, int r , int l)  //Cone     
•Void Area(int  pi, int r )  //Circle    
     
When and why to use method overriding    
•Its obvious that when we do inheritance between two classes, all the methods and properties of the first class are derived to the other class so that this becomes the child class which  adobes all the functionality of base class. It can also possesses its own separate methods.   
•But there is a big problem in inheriting the second class to the first class as it adobes all the methods same as the base class has, which  means that after inheritance both(base class& child class) have the methods of same name and same body as shown in this example 
•Example,  
 we have seen example of overriding
     
•how many overload of a method we can have?    
•    
•What?     
•Type?     
•When?     
•Overloading?    
•Overriding?     
•static binding? 
•Late binding?   
     
String and String Builder:   
•Strings are Immutable (Not Modifiable). If you try to modify the string it actually creates a new string and the old string will be then ready for garbage collection.   
•String Builder when instantiated, creates a new string with predefined capacity and up to that capacity it can accommodate string without needing to create a new memory location for the string....i mean it is modifiable and can also grow as and when needed.  
•The most common operation with a string is concatenation. This activity has to be performed very efficiently. When we use the "String" object to concatenate two strings, the first string is combined to the other string by creating a, and then the old string is deleted. This process is a little long. Hence we say "Strings are immutable".   
•When we make use of the "String Builder" object, the Append method is used. This means, an insertion is done on the existing string. Operation on String Builder object is faster than String operations, as the copy is done to the same location. Usage of String Builder is more efficient incase large amounts of string manipulations have to be performed. 
•String Example: 
   String myString=”Welcome”;
  myString=myString+”Software Team”;     
•String builder Example
    StringBuilder sb = new StringBuilder();    
        sb.Append("raj");    
        sb.Append("mani");   
     
String builder   
Methods:   
Ex:  
    Append, insert, remove, replace and Tostring.    
Performance:     
1.Avoid short appends. 
2.Cache objects. 
3.Avoid some data types.     
4.Data Types     
5.Append Chars   
6.Stringbuilder Comparison   
7.Append integers
8.Capacity 
●    
9.Example: 
  http://www.dotnetperls.com/stringbuilder     
     
     
Override: When a method of a base class is overridden in a derived class, the version in the derived class is used, even if the calling code didn't "know" that the object was an instance of the derived class.  
New: If you use the new keyword instead of override, the method in the derived class doesn't override the method in the base class, it merely hides it. 
If you don't specify either new or overrides, the resulting output is the same as if you specified new, but you'll also get a compiler warning (as you may not be aware that you're hiding a method in the base class method, or indeed you may have wanted to override it, and merely forgot to include the keyword).   
Override: used with virtual/abstract/override type of method in base class   
New: when base class has not declared method as virtual/abstract/override    
     
Static class , method  and variables     
     
12 Features of Static class  
1.A static class cannot be instantiated  
2.Static class can have only static members.   
3.Member of the Static class can be accessed by class name itself.     
4.Static class is sealed. So static class cannot be inherited.   
5.Static class contains only static constructors.    
6.Static class cannot have instance constructors.    
7.Static class can only be inherited only from object class.     
8.Static class is preceded by keyword static.  
9.Static constructor of static class called only once.     
10.Static class has private constructors 
11.Static classes cannot implement interfaces  
12.static classes cannot have instance constructors  
Notable Points here are:     
•A static method can be invoked directly from the class level    
•A static method not requires any class object 
•Any main() method is shared through entire class scope so it always appears with static keyword.   
Static method    
•A static method can access only static fields.
•A static method cannot access non static fields.    
•A static method cannot be called using object of a class  
•A static method can be called using class name.     
• Static field can be used using class name.   
•Static method cannot be override or overload. 
•We can't put access modifier in static constructor? 
Constructor:     
http://www.programcall.com/16/csnet/constructor-types-with-example-programs-in-csnet.aspx
     
•A static constructor does not take access modifiers or have parameters.     
•A static constructor is called automatically to initialize the class before the first instance is created or any static members are referenced.  
•A static constructor cannot be called directly.     
•The user has no control on when the static constructor is executed in the program.
•A typical use of static constructors is when the class is using a log file and the constructor is used to write entries to this file.   
•Static constructors are also useful when creating wrapper classes for unmanaged code, when the constructor can call theLoadLibrary method.
•If a static constructor throws an exception, the runtime will not invoke it a second time, and the type will remain uninitialized for the lifetime of the application domain in which your program is running.     
http://msdn.microsoft.com/en-us/library/k9x6w0hc.aspx
what is difference between instance constructor and Static constructor inC#.Net    
     
     
Main Differences are : 
• A Constructor declare using Static modifier was known as  Static Constructor. Rest of all were Instance Constructor.   
•Static Constructor are responsible for initialization of static variables and Instance Constructor for initialization of instance constructor.    
•A static constructor is called only one's in the execution of a class. Where as instance constructor gets called each time we create the object of the class. if no object is created. It is not called at all.     
•static constructor is the first block of which gets executed under the class.     
•A static constructor can't be parameterized because explicit calling of the constructor is not done.  
     
     
using System;    
using System.Collections.Generic;  
using System.Linq;     
using System.Text;     
namespace ConsoleApplication1{     
    class staticconstructor  
    {
        static staticconstructor() 
        {  
            Console.WriteLine("static constructor"); 
        }  
         staticconstructor()        {    
            Console.WriteLine("non-static constructor");   
        }  
        static void Main()   
        {  
            Console.WriteLine("main method");  
            staticconstructor st = new staticconstructor();
            staticconstructor st1 = new staticconstructor();     
            Console.ReadLine();    
        }  
    }
}     o/p: static constructor, main method  , non-static constructor , non-static constructor     
     
Notable Points here are:     
•A static method can be invoked directly from the class level    
•A static method not requires any class object 
•Any main() method is shared through entire class scope so it always appears with static keyword.   
Static method    
•A static method can access only static fields.
•A static method cannot access non static fields.    
•A static method cannot be called using object of a class  
•A static method can be called using class name.     
• Static field can be used using class name.   
•Static method cannot be override. 
•We can't put access modifier in static constructor? 
     
Access ViewState from Static method in aspx page     
     
You can get the reference to the page via HttpContext.CurrentHandler.  
public static string GetData(int CustomerID) { 
   Page page = HttpContext.Current.Handler as Page;  
   if (page != null)   
   { 
      string outputToReturn = "";  
      page.ViewState["MyVal"]="Hello";   
      return outputToReturn; 
      //btw, what a strange method!
   } 
}    
     
collection 
     
Four important categories    
•Index based     
–Array     
–List
•Key value pair  
–Hash table
–Sort list 
•Prioritized collection
–Queue     
–Stack     
•Specialized collection
–String collection     
–Hybrid dictionary     


array and array list
Array
Array List
1.System namespace
1.System.collection namespace
2.Char[] vowel=new char[];
2.Arraylist list =new arraylist()
3.Capacity of an array is fixed
3.Array list can increase and decrease size dynamically
4.It collection of same data type
4.It can hold different data type
5.Array can have multiple dimensions
5.Array list can have one dimension.
6.Ex:
6.Ex:
Hash Table and Array List
Hash Table
Array List
1.It is a dictionary
1.Collection of data
2.It is both index and key based
2.Index based
3.Hash table is a map
3.It is a list
4.Here we can add data with key
4.We can only add items to the list
5.Retrieving by key in hash table is faster than t\retrieving by array list
5.Here we can add any data type value, every item in array list is treated as object.
hash table

hashTable:
   HashTable stores a key-value pair type collection of data.
NOTE:
Both key and value are object
  the key values are UNIQUE
Functions:
•Clear
•Remove
•Containskey
•Containsvalue
•Contains
•Add
Variables
•Count

Remove:
hash_table_name.Remove(key);
Remove All Values:
hash_table_name.Clear()

ContainsKey(Key)

its returns true or false..
ContainsValue(value):
  its returns true or false..
EXAMPLE

Hashtable sampleHt  = New Hashtable
sampleHt.add("US",”united States”)  // Area- key.  1000 - valuesampleHt.add("IND",”India”)
        // To fetch the value we can use name, for example
        String countryname=convert.tostring(sampleHt[“US”]);
         sampleHt.remove(“US”);
         IDictionaryEnumerator  idic= sampleHt.GetEnumerator();
                    while(idic.MoveNext())
                    {
                        idic.Value.ToString();
                    }

Example 1:
// We cannot crate object for abstract class

using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace ConsoleApplication1
{
   public abstract class AbstactClass
    {
       public abstract string GetAbstractValue();
    }
    public class main1
    {
        static void Main(string[] args)
        {
            AbstactClass absObj = new AbstactClass();
          
        }
    }
}

Error  1      Cannot create an instance of the abstract class or interface 'ConsoleApplication1.AbstactClass'
Example 2:
// we cannot declare the abstract method in non abstract class

using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace ConsoleApplication1
{
   public class AbstactClass
    {
       public abstract string GetAbstractValue();
    }
    public class main1
    {
        static void Main(string[] args)
        {
            AbstactClass absObj = new AbstactClass();
          
        }
    }
}

Error:
'ConsoleApplication1.AbstactClass.GetAbstractValue()' is abstract but it is contained in non-abstract class 'ConsoleApplication1.AbstactClass'






Example 2:
// we cannot declare the non abstract method without definition

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace ConsoleApplication1
{
   public abstract class AbstactClass
    {
       public abstract void GetAbstractValue();
       public  void GetValue();

//       public  void GetValue(); // don’t throw error

//{}
      
    }
   public class Test : AbstactClass
   {
       public override void GetAbstractValue()
       {
       }
   }
    public class main1
    {
        static void Main(string[] args)
        {
            Test absObj = new Test();
            absObj.GetAbstractValue();
          
        }
    }
}


// We cannot declare a body in abstract method

public abstract class AbstactClass
    {
       public abstract void GetAbstractValue()
       {

       }
       public void GetValue()
       {
           Console.WriteLine("Get abstract method");
       }
        
      
    }




// Abstract, virtual method 

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace ConsoleApplication1
{
    public abstract class BaseClass
    {
        public abstract string GetAbstractValue();

        public virtual string GetVirtualValue()
        {
            return "Base GetVirtualValue";
        }

        public string GetValue()
        {
            return "Base GetValue";
        }
    }
    public class SubClass : BaseClass
    {
        public override string GetAbstractValue()
        {
            return "Sub Get Abstract Value";
        }
        public override string GetVirtualValue()
        {
            return "Sub GetVirtualValue";
        }
        public string GetValue() //new
        {
            return "Concrete GetValue";
        }
    }
    class Test
    {
        static void Main(string[] args)
        {
            BaseClass instance1 = new SubClass();
            Console.WriteLine(instance1.GetAbstractValue());
            Console.WriteLine(instance1.GetVirtualValue());
            Console.WriteLine(instance1.GetValue());

            SubClass instance2 = new SubClass();
            Console.WriteLine(instance2.GetAbstractValue());
            Console.WriteLine(instance2.GetVirtualValue());
            Console.WriteLine(instance2.GetValue());

            Console.Read();
        }
    }
}


//Since you cannot use abstract class for already inherited class. But you can use interface for already inherited class.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace ConsoleApplication1
{
    public interface inrefacename
    {
        void somemethod();

    }
  
    public abstract class BaseClass
    {
        public abstract string GetAbstractValue();

        public virtual string GetVirtualValue()
        {
            return "Base GetVirtualValue";
        }

        public string GetValue()
        {
            return "Base GetValue";
        }
    }
   public class classtest
    {

        public string GetValue1()
        {
            return "Base GetValue";
        }
    }
   public class classtest1 : classtest, inrefacename  // baseclass – abstract class (will not use abstract class)
   {

       public string GetValue4()
       {
           return "Base GetValue";
       }
      public  void somemethod()
       {
           Console.WriteLine("somemethod");
       }
   }
   public class SubClass : BaseClass
    {
        public override string GetAbstractValue()
        {
            return "Sub Get Abstract Value";
        }
        public override string GetVirtualValue()
        {
            return "Sub GetVirtualValue";
        }
        public  string GetValue()  //new
        {
            return "Concrete GetValue";
        }
    }
    class Test
    {
        static void Main(string[] args)
        {
            BaseClass instance1 = new SubClass();
            Console.WriteLine(instance1.GetAbstractValue());
            Console.WriteLine(instance1.GetVirtualValue());
            Console.WriteLine(instance1.GetValue());

            SubClass instance2 = new SubClass();
            Console.WriteLine(instance2.GetAbstractValue());
            Console.WriteLine(instance2.GetVirtualValue());
            Console.WriteLine(instance2.GetValue());

            Console.Read();
        }
    }
}


// Implementing few methods of a interface class-C#

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace ConsoleApplication1
{
    public interface IMyInterface
    {
        void SomeMethod();
        void SomeOtherMethod();
    }
    public abstract class MyClass : IMyInterface
    {
        // Really implementing this
        public void SomeMethod()
        {
            // ...
        }

        // Derived class must implement this
        public abstract void SomeOtherMethod();
    }
    class Test
    {
        static void Main(string[] args)
        {

            Console.Read();
        }
    }
}



// Achieve multiple inheritance concept via interface

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace ConsoleApplication1
{
    public interface IA1
    {
        void m2();
        void m();

    }

    public interface IA2
    {
        void m2();
    }

    public class CA : IA1, IA2
    {
        public void m()
        {
        }

        public void m2()
        {
            Console.WriteLine("A");
        }
    }
    public class CA1 : CA
    {
        public void m()
        {
        }

        public void m2()
        {
            Console.WriteLine("B");
        }
    }
    public class main1
    {
        static void Main(string[] args)
        {
            CA c1 = new CA();
            c1.m();
            c1.m2();
            CA1 ca1 = new CA1();
            ca1.m();
            ca1.m2();
            Console.Read();
        }
    }
}

// Dynamic Binding (hiding)

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace ConsoleApplication1
{
    class A
    {
        public virtual void WhoAreYou() { Console.WriteLine("I am an A"); }
        public virtual void WhoAreYou1() { Console.WriteLine("I am an A1"); }
        public virtual void WhoAreYou2() { Console.WriteLine("I am an A2"); }
    }
    class B : A
    {
        public override void WhoAreYou() { Console.WriteLine("I am a B"); }
    }
    class C : B
    {
        public new virtual void WhoAreYou() { Console.WriteLine("I am a C"); }
        //  public override void WhoAreYou1() { Console.WriteLine("I am an C1"); }
        public override void WhoAreYou2() { Console.WriteLine("I am an C2"); }

    }
    class D : C
    {
        public override void WhoAreYou() { Console.WriteLine("I am a D"); }
        public override void WhoAreYou2() { Console.WriteLine("I am an D2"); }
    }


    class Test
    {
        static void Main(string[] args)
        {

            C c = new D();  // where to extend C class in D
            c.WhoAreYou();// "I am a D"
            A a = new D();    // where to extend A class in B
            a.WhoAreYou();// "I am a B"

            A a1 = new D();  // No extend - virtual method
            a1.WhoAreYou1(); // "I am a A1"

            B a2 = new C();  // where to extend b class in c
            a2.WhoAreYou2(); // "I am a C2"

            B a3 = new D(); // where to extend b class in c
            a3.WhoAreYou2(); // "I am a D2"

            Console.ReadLine();

        }
    }

}


Sealed Class:
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace ConsoleApplication1
{
    public sealed class classsealed
    {
        public string ID;
        public double Price;
        public string GetValue()
        {
            return "Sealed class";
        }
    }
    //public class subsealedclasss : classsealed
    //{
    //    public string subsealedmethod()
    //    {
    //        return "subSealed class";
    //    }

    //}
    class Test
    {
        static void Main(string[] args)
        {
            classsealed sealedobject = new classsealed();
            Console.WriteLine(sealedobject.GetValue());
            sealedobject.ID = "10";
            sealedobject.Price = 12.23;
            //subsealedclassssubsealedobject = new subsealedclasss();
            //subsealedobject.subsealedmethod();
            Console.Read();


        }
    }

}

// Static Class
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace ConsoleApplication1
{
    public static class staticclass   // : object //7. Static class can only be inherited only from object class
    {
        // int a; // 2.    Static class can have only static members.
        static int i=1; // access
        //public void method()  // Static class can have only static method.
        //{
        //    Console.WriteLine("Test method");
        //}
        public static void method1()
        {
            Console.WriteLine("Test static method");
            Console.WriteLine(i);
        }
        //staticclass()  // static classess cannot have instance constructors
        //{
       //  Console.WriteLine("instance constructor");
        //}
        static staticclass()
        {
            Console.WriteLine("static constructor");
        }


    }
    public class Bus
    {
        // Static constructor:
        static Bus()
        {
            System.Console.WriteLine("The static constructor invoked.");
        }

     
        public static void Drive()
        {
            System.Console.WriteLine("The Drive method invoked.");
        }
    }

    //public class Testclass : staticclass   // 4.     Static class is sealed. So static class cannot be inherited
    //{
    //}
    class Test
    {
        static void Main(string[] args)
        {
            //   staticclass obj = new staticclass();  // static class cannot be instantiated
            staticclass.method1(); // first constructor only executed
            //staticclass.i = 6;
          
            Bus.Drive();
            Console.ReadLine();
        }
    }
}





// static method
public class Bus
{
    // Static constructor:
    static Bus()
    {
        System.Console.WriteLine("The static constructor invoked.");
    }

    public static void Drive()
    {
        System.Console.WriteLine("The Drive method invoked.");
    }
}

class TestBus
{
    static void Main()
    {
        Bus.Drive();
    }
}
// A static constructor is called automatically to initialize and first called

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace ConsoleApplication1
{
  
        class Program
        {

            static void Main(string[] args)
            {
                Child t = new Child();
            }
        }

        class Parent
        {
            public Parent()
            {
                Console.WriteLine("Parent Instance Constructor");
                Console.ReadKey();
            }

            static Parent()
            {
                Console.WriteLine("Parent Static Constructor");
                Console.ReadKey();
            }
        }
        class Child : Parent
        {
            public Child()
            {
                Console.WriteLine("Child Instance Constructor");
                Console.ReadKey();
            }

            static Child()
            {
                Console.WriteLine("Child Static Constructor");
                Console.ReadKey();
            }
        }
   
}


Output:
Child Static Constructor
Parent Static Constructor
Parent Instance Constructor
Child Instance Constructor



// Hash table

HashTable:
HashTable stores a key-value pair type collection of data. 
NOTE: 
Both key and value are object 
the key values are UNIQUE 
Functions:
1.     Clear
2.     Remove
3.     Containskey
4.     Containsvalue
5.     Contains
6.     Add
Variables
1.     Count

Remove:

hash_table_name.Remove(key);
Remove All Values:

hash_table_name.Clear()
ContainsKey(Key)


its returns true or false.. 
ContainsValue(value): 
EXAMPLE
Hashtable sampleHt  = New Hashtable
sampleHt.add("US",”united States”)  // Area- key.  1000 - value
sampleHt.add("IND",”India”) 
// To fetch the value we can use name, for example
String countryname=convert.tostring(sampleHt[“US”]);
sampleHt.remove(“US”);
IDictionaryEnumerator  idic= sampleHt.GetEnumerator();


                    while(idic.MoveNext())
                    {
                        idic.Value.ToString();
                    }










// Why c# not support multiple inheritance?

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace ConsoleApplication1
{
    class A
    {
        protected void samplemethod();
    }
    class B
    {
        protected void samplemethod();

    }
    class C : A, B
    {
    }
    class Test
    {
        static void Main(string[] args)
        {
            C obj = new C();
            obj.samplemethod(); // here which method to call now A or B?
        }
    }
}







Interface with objects:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace ConsoleApplication1
{
    public interface IMyInterface
    {
        void SomeMethod();
        void SomeOtherMethod();
    }
    public class MyClass : IMyInterface
    {
        // Really implementing this
        public void SomeMethod()
        {
            Console.WriteLine("Interface object");
        }

        // Derived class must implement this
        public void SomeOtherMethod()
        {
        }
    }
    class Test
    {
        static void Main(string[] args)
        {
            IMyInterface obj = new MyClass();
            obj.SomeMethod();
           

            Console.ReadLine();

        }
    }

}





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