Method overloading with Parent and Child class as parameter [duplicate]

Question

I have 3 classes GrandParent, Parent and Child, where Child extends Parent and Parent extends GrandParent

public class Main {
    void test(GrandParent gp){System.out.println("GrandParent");}
    void test(Parent p){System.out.println("Parent");}

    public static void main(String args[]){
        GrandParent obj = new Child();
        Main mainObj = new Main();
        mainObj.test(obj);  // This calls test(GrandParent gp)

        mainObj.test(new Child()); // This calss test(Parent gp)
    }
}

In above code in the 2 calls to test() method both with Child object calls different methods. In one it's doing compile-time and in other run-time binding. This sounds little weird to me. How would you explain this?

Answer 1

Method overloading is compile-time polymorphism.

Method overriding is runtime polymorphism.

In your case, you are overloading two instance methods of class Main.

However, since I presume in your context Child extends Parent, new Child() instanceof Parent == true hence an instance of Child is a valid argument for the method test with argument type Parent.

In your first case, you pass a reference type GrandParent in the method test, and the exact type is found.

In your second case, you pass a reference type Child in the method test. The closest match is Parent, hence test(Parent p) is invoked.