How null object can still return its property value?

Question

Below is my code. I set the object to null, still my print statement can print the property name correctly. Can anyone tell me what's happening?

public class MyClass {
    String name;

    public String getName() {
        return name;
    }

    public void setName(String s) {
        name = s;
    }
    public static void main(String args[]) {
        MyClass obj = new MyClass();
        obj.changeName(obj);

        System.out.println("Name = " + obj.getName());
    }
    public MyClass() {
        name = "A";
    }

    public void changeName(MyClass obj) {
         obj.setName("B");
         obj = null;
    }
}

Output is:

Name = B

score 4 · Accepted Answer · answered Dec 31 '17 at 07:26

4

obj = null only sets the local variable obj of the method changeName to null. It doesn't affect the object referenced by that variable in any way.

answered Dec 31 '17 at 07:26

Eran

387,369
54
702
768

3

Or the variable whose value was passed by value as a parameter to the method. – user207421 Dec 31 '17 at 07:37
1

Then how come obj.SetName sets to the property of the original object instead of local variable? – Sunil Dec 31 '17 at 09:03
1

@Sunil the local variable `obj` holds a reference to the original object, so `obj.setName("B")` is equivalent to `this.setName("B")`. – Eran Dec 31 '17 at 09:05
1

Ok. Got it thanks. Upvoted. – Sunil Dec 31 '17 at 09:07

score -1 · Answer 2 · answered Dec 31 '17 at 07:36

I apologize if this incorrect, I have been working with Kotlin lately and it’s messing with my head.

I would try either

 public void changeName(MyClass obj) {
     obj.setName("B");
     obj.setName(null);
}

Or you might try

 public void changeName(MyClass obj) {
     obj.setName("B");
     obj.setName().empty;
}

I think it has something to do with the fact your passing an object to that method and setting the value of the object and the null must be either nulling the incorrect object or the setName value is still holding its value even though the object itself is null. So you need to set the setName value to null I think.

You might also try making the method return an object? Then you could receive that object and null it at that point? — Vahalaru, Dec 31 '17 at 07:37

How null object can still return its property value?

2 Answers2