what is the need to declare a class abstract if it doesn't contain abstract methods?

[preethi kumar]

can anyone tell me?

[Hunter McMillen]

Abstract classes can't be instantiated(you can't create objects of their type), but they can be subclassed. Which means that another class could inherit all of its methods and attributes; whether those methods are abstract or not is up to the designer.

Example: Assume Java doesn't actually have a Math class

    
abstract public class Shape
{
     final double PI = 3.14;
}

public class Circle extends Shape
{
     public double getArea(int radius)
     {
          return super.PI * radius * radius;
     }

    public double getCircumference(int radius)
    {
         return 2*super.PI * radius;
    }
}

The PI constant in the shape class can be used by the Circle class. This is a poor example because Java provides a Math class that holds constants like PI.

Sun examples:
http://java.sun.com/docs/books/tutorial/java/IandI/abstract.html

Hunter

[preethi kumar]

we could have done the same thing without declaring the shape class abstract right?

whats is the difference it made?

[Hunter McMillen]

You could have yes. But in this case Shape was abstract because you wouldn't just want to create a generic Shape object. You wouldnt know how to find the volume of a "Shape", or its circumference, etc..


Hunter

[Bear Bibeault]

Remember, just because you can do something doesn't mean that you should.

[marc weber]

Bear Bibeault wrote:Remember, just because you can do something doesn't mean that you should.

I can reply to this.

[preethi kumar]

thank you so much

[preethi kumar]

ya marc you can reply