What is the output for the following Java program where null is passed as argument for the overloaded methods?

Question

public class Overloading {
    public static void main(String[] args) {
        Overloading o = new Overloading();
        o.display(null);
    }
    void display(String s) {
        System.out.println("String method called");
    }
    void display(Object obj) {
        System.out.println("Object method called");
    }
}

It is giving the output as "String method called". I need the explanation why?

Yeah..It is giving the output as "String method called". I need the explanation why? — vinod kumar, Oct 29 '13 at 15:22
I answered a similar question earlier. Please see the question I flag this one as duplicate of. — Miserable Variable, Oct 29 '13 at 15:28
This question has been asked numerous times before. Please do some searching first. — arshajii, Oct 29 '13 at 15:29
@Stieffers `null` is not an `Object`, but it is a [literal](http://docs.oracle.com/javase/specs/jls/se7/html/jls-3.html#jls-3.10.7) and has its own `type`. — Miserable Variable, Oct 29 '13 at 15:30

noone · Accepted Answer · 2013-10-29T17:31:18.717

5

Taken from the Java Spec:

If more than one member method is both accessible and applicable to a method invocation, it is necessary to choose one to provide the descriptor for the run-time method dispatch. The Java programming language uses the rule that the most specific method is chosen.

First of all: both methods are accessible (obviously) and applicable. They are both applicable, because null is of type nulltype, which is by definition a subtype of all types. String is more specific than Object, because String extends Object. If you would add the following, you will have a problem, because both Integer and String are equally "specific":

void display(Integer s) {
    System.out.println("Integer method called");
}

edited Oct 29 '13 at 17:31

answered Oct 29 '13 at 15:28

noone

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I find this explanation incomplete without describing null-type which for the purpose of overload resolution is considered to be subtype of all other types. – Miserable Variable Oct 29 '13 at 17:25
@MiserableVariable Good point, I added it. – noone Oct 29 '13 at 17:32

score 4 · Answer 2 · answered Oct 29 '13 at 15:28

4

Java will always find the most specific version of method that is available.

String extends Object, and therefore it is more specific.

http://docs.oracle.com/javase/specs/jls/se7/html/jls-15.html#jls-15.12.2.5

answered Oct 29 '13 at 15:28

Oh Chin Boon

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What is the output for the following Java program where null is passed as argument for the overloaded methods?

2 Answers2