Dictionary is used to represent a collection of key and Value pair of data. It is a generic class and it can store any data type. It came with .net F/W 2.0.

Dictionary contains key and value together as shown in given example below

 protected void Page_Load(object sender, EventArgs e)
    {
        Dictionary<string, int> Emps = new Dictionary<string, int>();
        Emps.Add("Ram", 1);
        Emps.Add("Mohan", 2);
        Emps.Add("Hari", 3);
        foreach (var name in Emps)
        {
            lblmsg.Text += name.Key + " " + name.Value  +"<br>";
        }     
    }

Then output will come like this

Ram 1
Mohan 2
Hari 3

ContainKey and ContainValue Method

It has containkey and ContainValue method. Using ContainKey we can find the specific key in dictionary and using ContainValue we can get the specific value. It returns the Boolean value.

 if(Emps.ContainsKey("Hari"))
        {
            int value = Emps["Hari"];
            lblmsg.Text = value.ToString();
        }

It has also add,remove and Clear method.

Advantages

1. Dictionary type provides fast lookups with keys to get values.
2. It stores any datatype
3. It provide good performance as compare to HashTable

Hi
This is one of the frequently asked questions in interview. I have faced this question in almost in all interviews. So let’s understand what is abstract class?

Abstract class is the class which one cannot be instantiated. This means we canot create object of this class like general class. To use it, we need to inherit it. It contains the abstract keyword.

In abstract class, we can define
1. Normal Property
2. Abstract Property
3. Normal Method
4. Abstract Method
5. Virtual method.

Now let see this concept with example

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;

/// <summary>
/// Summary description for Class1
/// </summary>
public abstract class Class1
{
    public virtual string SayHello()
    {
        return "Hello from virual method";
    }

    public string sayHello2()
    {
        return "I m from SayHello Method";
    }

    public abstract string SayHello1();

}

Note: Here i have created the abstract class which contain Normal method,abstract method and Virtual method.

Now we will inherit this class in class2 like this

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;

/// <summary>
/// Summary description for Class2
/// </summary>
public class Class2:Class1
{
    public override string SayHello()
    {
        return "This is the orveride message using virtual method";
    }

    public override string SayHello1()
    {
        return "This is the orveride message using abstract message";
    }


}

Note: in the above code i have override the virtual and abstract method. So if virtual or abstract keyword is there then we have to must override it.

Now we will call this method in default.cs page like this on button click event

 protected void Button1_Click(object sender, EventArgs e)
    {
         Class2 obj = new Class2();
       
        Response.Write(obj.SayHello()+"<br>"); 
        Response.Write(obj.SayHello1()); 
        
    }

Now compile the code, we will get output like this

When to use abstract Class?

We can use this class in this senario

1. If we have created some class and we want to modify some methods with new feature and we have to use somewhere then we can use abstract class

2. If we are developing some product type project, where we have to keep on adding new features in coming days then we can use abstract class.

Note: This is all my understanding my abstract class, if you feel i missing some important point then let me know. You are always welcome.