abstract sub-class

[feniger]

is this possible in java?
abstract class A extends B () {...}

[sukatoa]

Yep,

Here is an example,

Code:

public class test extends B{

	public test(){
		this.printA();
		this.printB();
	}

	public static void main(String args[]){
		new test().printA();
	}
}

abstract class B extends A{
	public void printA(){
		System.out.println("class B");
	}		
}

abstract class A{
	public void printB(){
		System.out.println("class A");
	}
}

Guess the output....

[Eranga]

feniger got a nice example.

As that example, you have keep in mind two things.

1. Abstract class can be subclassed, as you can see.

2. Abstract classes cannot instantiate. If you do such a things, in compile time, got an error that abstract class cannot be instantiate.

[danielstoner]

At any level in the class hierarchy you can declare an abstract class.

Code:

package jf.acls;

public class Concrete {
    @Override
    public String toString() {
        return "Concrete";
    }
}

package jf.acls;

public abstract class Abstract extends Concrete {
    @Override
    public String toString() {
        return "Abstract extends Concrete";
    }

    public abstract int getTheNumber();
}

[Eranga]

Quote:

Originally Posted by danielstoner

At any level in the class hierarchy you can declare an abstract class.

Code:

package jf.acls;

public class Concrete {
    @Override
    public String toString() {
        return "Concrete";
    }
}

package jf.acls;

public abstract class Abstract extends Concrete {
    @Override
    public String toString() {
        return "Abstract extends Concrete";
    }

    public abstract int getTheNumber();
}

Nice explanation though. I have one confusion here. What you mean any level of class hierarchy. I'm confusing it with your code.

[danielstoner]

I think his question was if it is possible to extend a concrete class (non-abstract) with an abstract class. And I said yes Abstract extends Concrete. I just wanted to make it clear that an abstract class can exist lower in the hierarchy, not only at the top. I hope it is clear now because if I continue to explain it will become really messy and unclear. LOL

[Eranga]

Sure, I got the point. Thanks.