ArrayList index is always 0 (zero)

Question

i have a problem with ArrayLists in Java. The problem is that when i add an element to the list (pointStorer), the index doesn't increment and every time it resets and remains zero. Here's my code (well it's only the important part of the code):

private ArrayList pointStorer = new ArrayList();
private Point pointValues = new Point();

public void mouseClicked(MouseEvent e) {

    pointValues.setLocation(e.getX(), e.getY());
    mousePointX = pointValues.x;
    mousePointY = pointValues.y;

    repaint();
}

public void paint(Graphics g){

        pointStorer.add(pointValues);

        System.out.println("Index point "+pointStorer.indexOf(pointValues));


}

I use the method .indexOf to know what's the index of the element that i've just added, but it remains always zero.

Thank you in advance for your help.

Do you have only a single Point instance, do you create it only once and then assign values to it multiple times? — Krzysztof Krasoń, May 24 '16 at 19:21

score 9 · Accepted Answer · answered May 24 '16 at 19:21

9

You only have one Point instance which you keep adding to the ArrayList, so all the indices of the ArrayList contain the same Point.

To add a new Point each time the mouse is clicked, you should create a new Point instance :

public void mouseClicked(MouseEvent e) {

    Point pointValues = new Point();
    pointValues.setLocation(e.getX(), e.getY());
    mousePointX = pointValues.x;
    mousePointY = pointValues.y;

    repaint();
}

answered May 24 '16 at 19:21

Eran

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702
768

Ahh you're right! It worked! Thank you so much! – HeyMan May 24 '16 at 19:32

score 0 · Answer 2 · answered May 24 '16 at 19:24

0

You should instantiate your pointStorer variable inside your paint() method

answered May 24 '16 at 19:24

tfosra

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12

ArrayList index is always 0 (zero)

2 Answers2