Question

While studying C# in ASP.net I have trouble understanding several classes. In which scenario should I use the following classes private,public,protected,abstract,static,sealed ?

It would be better if someone can explain these with easy examples.

Answer 1

Those are not classes.

private, protected and public are access modifiers. They indicate which other code can see the code they affect:

public class Foo
{
    private int _myOwn = 1;
    protected int _mineAndChildren = 2;
    public int _everyOnes = 3;
}

public class Bar : Foo
{
    public void Method()
    {
        _myOwn = 2; // Illegal - can't access private member
        _mineAndChildren = 3; // Works
        _everyOnes = 4; // Works
    }
}

public class Unrelated
{
    public void Method()
    {
        Foo instance = new Foo();
        instance._myOwn = 2; // Illegal - can't access private member
        instance._mineAndChildren = 3; // Illegal
        instance._everyOnes = 4; // Works
    }
}

An abstract class is one that may contain abstract members. An abstract member has no implementation, so all derived classes must implement the abstract members.

A sealed class cannot be inherited. A static class is sealed, but also can only contain static members.

I suggest you start with “Getting Started with Visual C#. This is a very basic question.