using instanceof operator in Java

Question

I have a base class called class Base and two children classes

class A extends Base

and

class B extends Base

I have a method foo in Base.

Rather than putting the implementation of foo in class A and class B, so that I can do

void foo (Object o)
{
    // A's implementation
    assert o instanceof A;     
}


 void foo (Object o)
 {
     // B's implementation
     assert o instanceof B; 
 }

Is there anyway to put foo in Base, and still still be able to check for the runtime class? I've thought of something like this:

 void foo (Object o)
 {
    // Check that o is instanceof a runtime class
    assert o instanceof this.getClass(); // ????
 }

Thanks.

Answer 1

You can implement your method like this:

public void foo() {
    if (this instanceof A) {
        // implementation for A
    }
    else if (this instanceof B) {
        // implementation for B
    }
}

But the point of polymorphism is to put the A implementation in A, so that this implementation can use A's private fields to implement the method (same for B, or course).