A question about runtime polymorphism.

[Dmitry Zhuravlev]

Here is the code:

class A {
    void printthem() {
        printit();
    }
   private void printit() {
        System.out.println("A");
    }
}

class B extends A {
    void printit() {
        System.out.println("B");
    }
}  

public class Main {
public static void main(String[] args) {
    A a = new A();
    B b = new B();
    A ab = new B();

    a.printthem();
    b.printthem();
    ab.printthem();
}
}  

And here is the output:

A
A
A

I wonder why it doesn't print B at second and third lines?

[Sridhar Gudipalli]

Because class A's printthem() method doesnot know anything about class B's printit() method as A's printit() method is private.

[Ankit Garg]

As Sridhar said, printit method in A is private and private methods are not overridden so the call to printit is not polymorphic as printit in B doesn't override printit of A...

[Jim Hoglund]

So just to remind myself:
1) Private methods are not overridden / polymorphic
2) Static methods are not overridden / polymorphic

Jim ... ...

[Sahil Kapoor]

1) Class B's printit() method is NOT overriding Class A's printit() method because of the fact that Class A's method is Private.

2) Polymorphism applies only to overriden methods and not overloaded or redefined methods.

3) Had it been the case that Class A defines printit() method to be public , then the output at second line would definitely be B, because at that time Class B overrides prinit() method and polymorphism applies to it.


Thanks !!!