Re: About abstract class and abstract method

Sameer schrieb: 
Consider the declaration from Java API:

public abstract class Toolkit extends Object

This abstract class java.awt.Toolkit contains one abstract method beep.

public abstract void beep()

The Java Tutorial says that-
"An abstract class can contain abstract methods - methods with no
implementation. In this way, an abstract class can define a complete
programming interface for its subclasses but allows its subclasses to
fill in the implementation details of those methods."

But we can make instance of Toolkit and make use of this method.
Toolkit t= new Toolkit();
> t.beep();
You can *not* do this. The compiler-error is "Class java.awt.Toolkit is abstract and therefore cannot be instantiated" 

How can we make instance of this abstract class and make use of one of
its abstract method?
Who fill 'implementation details' for the beep method?
You can do for example:
Toolkit t= Toolkit.getDefaultToolkit();
t.beep();
You will get a non-abstract subclass of java.awt.Toolkit here.
On Windows you get a sun.awt.windows.WToolkit, which has an implementation for beep()


-Sameer



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