Which method is chosen in a polymorphism when calling a method available in the parent and the child class?

user_7293065 0
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I don't understand why the ab.m3() method calls the function of the parent class and not the child. I thought maybe passing a new Integer to the method might call the method of the parent class because Integer is an Object so I tried it with an int but still it gave me the same result!

public class A {

    public void m1(){
        System.out.println("A.m1");
    }
    public void m2(){
        System.out.println("A.m2");
    }
    public void m3(Object x){
        System.out.println("A.m3");
    }
}

public class B extends A{

    public void m1(){
        System.out.println("B.m1");
    }
    public void m2(int x){
        System.out.println("B.m2");
    }
    public void m3(int x){
        System.out.println("B.m3");
    }

    public static void main(String[] argv){
        A aa = new A();
        A ab = new B();

        int num = 2;

        ab.m1();
        ab.m2();
        ab.m3(new Integer(2));
        ab.m3(num);

    }
}

Output:

B.m1
A.m2
A.m3
A.m3
polymorphism java
2 Answers

B.m3 does not override A.m3, because the parameter lists are not compatible.

Because the only matching method in A is A.m3, and because there is no override in B, it is A.m3 that will be called.

user_68151310

Your ab reference is of type A.

When compiling ab.m3(num);, the compiler isn't looking at the object type. In general, it won't always know what the object type is. Instead, it's looking at the reference type. It cannot match B.m3(int), because the reference type is not of type B.

So the compiler chooses the A.m3(Object) method, which could be overridden at runtime. But it's not, so the A implementation is called.

user_2020090
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