Question

class A{}
class Z{}
class S{}

public class Demo6 {

    void fun(A a){
        System.out.println("A reference");
    }

    void fun(Z z){
        System.out.println("Z reference");
    }

    void fun(Object o){
        System.out.println("other reference");
    }

    public static void main(String args[]){
        new Demo6().fun(new A());
        new Demo6().fun(new S());
    }   
}

Output of the above code is coming:

A reference

other reference

My confusion is how “other reference” is printing when we are passing ‘S’ class object. Elaborate the actual mechanism of how ‘S’ class object is compatible with the “Object” class.

Answer 1

Every class has java.lang.Object as a parent – even if you don’t write extends Object, the compiler adds it automatically. To quote the javadoc:

Class Object is the root of the class hierarchy. Every class has Object as a superclass. All objects, including arrays, implement the methods of this class.

S obviously exists, otherwise it wouldn’t compile. Then the compiler chooses the most specific method to invoke. S does not match the signatures with neither Z nor A, and it matches the Object one.