Java graphics behaving strange

Question

I'm making a program in which you can click on a JLabel which holds an image and circles will appear on the JLabel. This works flawless on my macintosh/java6 but when I'm using windows/java7 all sorts of weird things happens. On some parts of the image you can't draw a circle. It's like an invisible square in the middle of the picture. And sometimes the circles disappear and come back at different times. Everytime i draw a new circle all the circles are getting redrawn on top of the label.

public void paint(JComponent label) {
    Graphics g = label.getGraphics();
    for (T node : nodes.keySet()) {
        Point p = nodes.get(node);
        Color color;
        if (p.selected) {
            color = Color.RED;
        } else {
            color = Color.BLUE;
        }
        g.setColor(color);
        g.fillOval(p.x, p.y, circleRadius*2, circleRadius*2);
        g.setColor(Color.BLACK);
        g.setFont(new Font("Helvetica", 20, 20));
        g.drawString((String) node, p.x, p.y);
    }       
}

Does anyone know what might cause this?

Answer 1

Never use getGraphics(), it can return null and at best is a snap shot of the last paint cycle

As soon as a repaint occurs anything painted to it will be removed

Instead, as Legend has already suggested, create yourself a custom label and override paintComponent and perform your painting here

Remember, painting is stateless, this means that on each repaint, you'll have to reconstruct your state

Take a look at Custom painting

Answer 2

Remove your paint(JComponent j); method and try using the following JLabel. Tweak as necessary to suit your needs.

final JLabel jLabel = new JLabel("!X!") {
    @Override
    public void paintComponent(final Graphics g) {
        super.paintComponent(g);
        for (T node : nodes.keySet()) {
            Point p = nodes.get(node);
            Color color;
            if (p.selected) {
                color = Color.RED;
            } else {
                color = Color.BLUE;
            }
            g.setColor(color);
            g.fillOval(p.x, p.y, circleRadius*2, circleRadius*2);
            g.setColor(Color.BLACK);
            g.setFont(new Font("Helvetica", 20, 20));
            g.drawString((String) node, p.x, p.y);
        }              
    }
};