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how to call an abstract class

Posted on 2002-06-15
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Last Modified: 2010-03-30
Hai

I want to know any way to call an abstract class by using Class c=Class.forName(abstract class);
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Question by:hellohowareu
7 Comments
 
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by:CEHJ
ID: 7080377
What would you want to do with 'c' as in Class c?
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flooder earned 400 total points
ID: 7080763
As I understand you can only inherit from a abstract class. The purpose of it is to define a structure, to which the other classes that inherit from it must comply to. So my answer would be is that you can't call a abstract class and wanting to do so would point to a flaw in design.
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by:objects
ID: 7080940
You can certainly create a Class instance for an abstract class, eg.

Class cls = Class.forName("java.awt.Graphics");

But you cannot create instances of an abstract class using any means.
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Expert Comment

by:Igor Bazarny
ID: 7083237
Hi,

You need to use Class.forName() only if you don't know class name at compile time. If you really need Class instance, you can use ClassName.class construct to get it. Depending on what you need, Class instance might be not necessary.

You can create instances of abstract classes, but this classes can be used to declare variables, method parameters etc.:

abstract class A{
    public anstract void someMethod();
    public void anotherMethod(){
    }
}

class B extends A{
    public void someMethod(){
    }
}

class User{
    A field;
    A methodReturningA(){
        return new B();
    }
    void methodReceivingA(A parameter){
        parameter.someMethod();
        parameter.anotherMethod();
    }
    void instanceofCheck(Object supposedToBeA){
        if( supposedToBeA instanceof A){
            A var = (A)supposedToBeA;
            var.someMethod();
        }
    }
}

Regards,
Igor Bazarny,
Brainbench MVP for Java 1
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Expert Comment

by:kylar
ID: 7084481
This is exactly what you wanted to know in your previous question.

http://www.experts-exchange.com/java/Q_20310654.html

As Objects and I both said, you can't instantiate an abstract class. Reflection or standard, it just won't work. You need to get a concrete subclass of the abstract class (make one up if it doesn't exist). then you can create it and reflect it as needed.

Cheers,
Kylar
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Expert Comment

by:kylar
ID: 7084491
Also, you have yet to close a question since joining, and have open, unlocked questions dating back 2.5 years.. It is bad etiquette not to follow up on your questions.

Cheers,
Kylar
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by:Mindphaser
ID: 7121670
Force accepted

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