通过传递0和null的Null参数的方法重载

Question

I have seen questions on Stack Overflow about a method overloading for null argument but didn't solve my confusion and I tried something different which was not discussed in there answers that's why asking this question.

I want the reason when I pass "null" it executes the function whose argument type is double and when I pass "0" or any other numeric digit like 1,2,10 etc to the function it executes the function whose argument type is "Object". I know there is a difference in NULL and 0 here is the difference.

Thanks!

Code:

public class NullArgumentOverloading {

    public static void main(String[] args) {

        NullArgumentOverloading obj = new NullArgumentOverloading();
        obj.overLoad(null); // prints "Double array argument method."
        obj.overLoad(0); // prints "Object o argument method."
    }

    private void overLoad(Object o) {
        System.out.println("Object o argument method.");
    }

    private void overLoad(double[] dArray) {
        System.out.println("Double array argument method.");
    }
}

Answer 1

Java will always try to use the most specific version of a method that's available (see JLS 15.12.2 ).

Object , double[] can both take null as a valid value. Therefore both are suitable.

Object is the super-type of double[] and therefore more specific than just Object . So thats the reason why it prints "Double array argument method." when you pass null to the function

For the ohter Question: As already explained in the comments, when you pass 0 which is a primitive int , will be boxed automatically into an Integer which have Object as super-type, so it prints "Object o argument method."

You can find more info in Method Overloading for null argument