Does null have Object type?

Question

Why does this output: "inside String argument method"? Isn't null "Object" type?

class A {
    void printVal(String obj) {
        System.out.println("inside String argument method");
    }

    void printVal(Object obj) {
        System.out.println("inside Object argument method");
    }

    public static void main(String[] args) {
        A a = new A();
        a.printVal(null);
    }
}

Wow crazy. I just tried adding a third `printVal` overload, `printVal(Integer obj)` to see what would happen. Now `a.printVal(null)` is a compiler error, due to ambiguity. Good question. — mgiuca, Feb 06 '11 at 01:55

score 8 · Answer 1 · edited May 23 '17 at 12:24

8

The most specific matching method will be called. More information here:

Which overload will get selected for null in Java?

edited May 23 '17 at 12:24

Community

1
1

answered Oct 13 '10 at 05:24

Gunslinger47

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score 3 · Accepted Answer · answered Oct 13 '10 at 05:36

3

Yes, but null is also String type and all other types, so it selects the most specific method to call.

answered Oct 13 '10 at 05:36

amara

2,216
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score 1 · Answer 3 · answered Oct 13 '10 at 17:22

More specifically, a null literal will call the String version, for the reasons outlined by the other answers.

On the other hand:

class A {
    void printVal(String obj) {
        System.out.println("inside String argument method");
    }

    void printVal(Object obj) {
        System.out.println("inside Object argument method");
    }

    public static void main(String[] args) {
        A a = new A();
        Object myObj = null;
        a.printVal(myObj);
    }
}

will print "inside Object argument method." As will settings the type for myObj to any type other than String.

Does null have Object type?

3 Answers3