/*
 * An abstract class can contain some common functionality, such as the 
 * "YouDontHaveToWriteThisFunctionAgain" method. This function can be called
 * from the class that inherits this AbstractTest class using the base keyword:
 * base.YouDontHaveToWriteThisFunctionAgain()
 * Also the class that inherits this AbstractTest class must implement the other
 * functions marked "abstract". That is, the inheriting class must define its
 * own function for those abstract members.
 */

public abstract class AbstractTestBase
{
    private const int m_multiplier = 2;

    // The class inheriting AbstractTestBase can call this function by using
    // the base keyword: base.YouDontHaveToWriteThisFunctionAgain()
    // If you don't intend to have a common, reusable function like this, then
    // you shouldn't use an abstract class. Instead, create an interface class.
    // NOTE: Use the "public" access modifier instead of "protected" if you want
    // to allow the implimenting class to have direct access to this function.
    protected int YouDontHaveToWriteThisFunctionAgain(int value)
    {
        return value * m_multiplier;
    }

    // The class inheriting this must implement the following function.
    // We don't care how it is implemented, just that it is implemented.
    public abstract void YouMustImplementThis();
}



// Now you can inherit from the AbstractTestBase class and use it like this:
public class TestAbstractClass : AbstractTestBase
{

    // The key feature of an abstract class is that you can re-use code from the base:
    public int WrapAndUseAnAbstractMethod(int value)
    {
        return base.YouDontHaveToWriteThisFunctionAgain(value);
    }

    public override void YouMustImplementThis()
    {
        // Add your code here for this function!
        throw new NotImplementedException("You have to write code here");
    }
}

AbstractClassExample

class, c#

C#