Get location of a swing component

Question

I have put some JPanels into another JPanel which its\' layout is Box Layout and Y-Axis. After I have put all the panels I need to get the Y position of each added JPanel in

Answer 1

Pack the frame before getting position. It seems everything overlaps each other starting at origin (0,0) until you pack.

Here's a working code:

import java.awt.Component;
import java.awt.Dimension;
import javax.swing.BoxLayout;
import javax.swing.JFrame;
import javax.swing.JPanel;

public class TestBoxLayout {

    public static void main(String[] args) {
        JFrame frame = new JFrame();

        JPanel panelHolder = new JPanel();
        panelHolder.setLayout(new BoxLayout(panelHolder, BoxLayout.Y_AXIS));

        for (int i = 0; i < 10; i++) {
            JPanel p = new JPanel();
            p.setPreferredSize(new Dimension(100, 13)); //I set the height just to make sure.
            panelHolder.add(p);
        }
        frame.add(panelHolder);

        /**
         * Pack before you get the position.
         */
        frame.pack();

        int componentCount = panelHolder.getComponentCount();
        for (int j = 0; j < componentCount; j++) {
            Component c = panelHolder.getComponent(j);
            JPanel p = (JPanel) c;
            System.out.println(p.getY());//I get 0, 13, 26, 39, .....
        }

        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setVisible(true);
    }
}

Result:

0
13
26
39
52
65
78
91
104
117

Note: The signature for BoxLayout is BoxLayout(Container target, int axis). The target is the stuff you are setting your layout to. For this reason, if you want use a BoxLayout, you should always create the panel first. Then use component.setLayout() so that the target already exists. The this in your JPanel constructor was referring to something else, not panelHolder. I guess the class you created this function in is also a subclass of Container and that is why you didn't get an error.