Aliasing doesn't work

Question

I created this class with the method addVertex:

public class Polygon {
    private PointNode _startPoint;

    public Polygon() {
        _startPoint = null;
    }

    public boolean addVertex(Point p, int pos) {
        PointNode next = _startPoint;
        int i = 0;
        while(i != pos){
            if(next == null)
                return false;
            next = next.getNext();
            i++;
        }
        next = new PointNode(p);
        return true;
    }
}

But the problem is that next doesn't alias with _startPoint and because of that I can only use the method when pos == 0 but if pos >= 1 then it always returns false even after I set a value in position 0 of the list I created.

Can someone tell me where the problem is?

If you mean that you expected changes to the `next` local variable to change the value of the `_startPoint` field, no, that won't happen - why did you think it would? — Jon Skeet, Feb 06 '15 at 15:00
This should work if you replace all references to `next` with references to `_startPoint`. — fzzfzzfzz, Feb 06 '15 at 15:03
Read the highly up-voted answers to this Q: http://stackoverflow.com/questions/40480/is-java-pass-by-reference-or-pass-by-value — Stephen C, Feb 06 '15 at 15:26

score 2 · Answer 1 · answered Feb 06 '15 at 15:06

In Java, you can't change what object a variable is pointing to other than by assigning another object to that exact variable with =. So, the only way to put another object to _startPoint is to actually do:

_startPoint = someOtherObject;

So, in Java, you can't give multiple names to a variable, as with PHP's & construct, for example.

Aliasing doesn't work

1 Answers1