SwingUtilities.convertPoint() returns negative values

Question

I am facing this issue in another project which has complicated JPanels structure and much code.

In there I have a following snippet

Point point = label.getLocation();
Point point2 = SwingUtilities.convertPoint(label.getParent(), point, panel);

in where label and panel are selected dynamically and JLabel is supposed to be grand-grand-...-child of JPanel.

So why question is in what case SwingUtilities.convertPoint() can return negative values if source and destination have child-parent relation? Is this possible at all?

This code demonstrated negative coordinates issue, but there panel22 is not parent of label.

import java.awt.BorderLayout;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Point;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;

public class NegativeLocation {
    public static void main(String[] args) {
        new NegativeLocation();
    }

    public NegativeLocation() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                JFrame frame = new JFrame();
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.setLayout(new BorderLayout());

                JPanel panel1 = new JPanel() {
                     @Override
                     public Dimension getPreferredSize() {
                         return new Dimension(600, 400);
                     }
                };

                JPanel panel21 = new JPanel() {
                    @Override
                    public Dimension getPreferredSize() {
                        return new Dimension(300, 400);
                    }
                };
                panel1.add(panel21);

                JPanel panel22 = new JPanel() {
                    @Override
                    public Dimension getPreferredSize() {
                        return new Dimension(300, 400);
                    }
                };
                panel1.add(panel22);

                JPanel panel3 = new JPanel() {
                    @Override
                    public Dimension getPreferredSize() {
                        return new Dimension(300, 400);
                    }
                };
                panel21.add(panel3);

                JLabel label = new JLabel("Label");
                panel3.add(label);

                frame.getContentPane().add(panel1);
                frame.setPreferredSize(new Dimension(600, 400));

                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);

                Point point = label.getLocation();
                Point point2 = SwingUtilities.convertPoint(label.getParent(), point, panel21);
                Point point3 = SwingUtilities.convertPoint(label.getParent(), point, panel22);

                System.out.println(point2);
                System.out.println(point3);
            }
        });
    }
}

So the output is

java.awt.Point[x=134,y=10]
java.awt.Point[x=134,y=-395]

UPD: Basically, I need to get location of label relative to panel21. How can I modify this line to achive it?

Point point = label.getLocation();
Point point2 = SwingUtilities.convertPoint(label.getParent(), point, panel21);

It's because you passed the location of the JLabel, but passed the labels parent, so the location information is now invalid — MadProgrammer, Dec 07 '12 at 08:15
@MadProgrammer but `getLocation()` gives result relative to parent. So I specify parent as source. What's wrong with my logic? — Nikolay Kuznetsov, Dec 07 '12 at 08:17
But the convert location method expects the location of the child in the child's coordinate space, not the parents — MadProgrammer, Dec 07 '12 at 08:21
@MadProgrammer so `Point point2 = SwingUtilities.convertPoint(label, new Point(0,0), panel21);` ? — Nikolay Kuznetsov, Dec 07 '12 at 08:44
That would be more correct, it would convert the point 0x0 from the `label`'s coordinate space to the coordinate space `panel21` — MadProgrammer, Dec 07 '12 at 08:53

score 7 · Answer 1 · answered Dec 07 '12 at 08:14

7

For me it's correct behaviour. Imagine following. Main panel contains a child with location x=0 y=100. If you convert the main panel 0,0 point to the child it returns us 0, -100. In fact it doesn't matter which component is parent of which. The logic is to add (all subtract) all translate() calls which are applied to graphics when parent renders child.

answered Dec 07 '12 at 08:14

StanislavL

56,971
9
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@Nikolay Kuznetsov did you tried to add different colors as JPanel.setBackground and then to resize of JFrame, now I understand after Stas replied, coordinates are correct, you linked Point to another JPanel (not parent, then there is negative amount :-) – mKorbel Dec 07 '12 at 08:26
@mKorbel and Stas, please see my update, I need to get location of label relative to panel21. Is my approach correct? – Nikolay Kuznetsov Dec 07 '12 at 08:45
I think the approach you mentioned above is correct Point point2 = SwingUtilities.convertPoint(label, new Point(0,0), panel21); – StanislavL Dec 08 '12 at 05:54

MadProgrammer · Accepted Answer · 2012-12-07T08:52:40.663

Take the following example...

enter image description here

public class TestLocation01 {

    public static void main(String[] args) {
        new TestLocation01();
    }

    public TestLocation01() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
                }

                JPanel outter = new JPanel(new BorderLayout());
                outter.setBorder(new CompoundBorder(new LineBorder(Color.RED), new EmptyBorder(10, 10, 10, 10)));
                JPanel inner = new JPanel(new GridBagLayout());
                inner.setBorder(new CompoundBorder(new LineBorder(Color.BLUE), new EmptyBorder(10, 10, 10, 10)));
                JLabel label = new JLabel("Testing");
                inner.add(label);
                outter.add(inner);

                JLabel below = new JLabel("Below");

                JFrame frame = new JFrame("Test");
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.setLayout(new BorderLayout());
                frame.add(outter);
                frame.add(below, BorderLayout.SOUTH);
                frame.setSize(200, 200);
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);

                System.out.println("lable.location: " + label.getLocation());
                System.out.println("label to inner: " + SwingUtilities.convertPoint(label, new Point(0, 0), inner));
                System.out.println("label to outter: " + SwingUtilities.convertPoint(label, new Point(0, 0), outter));
                System.out.println("label.parent to inner: " + SwingUtilities.convertPoint(label.getParent(), new Point(0, 0), inner));
                System.out.println("label.parent to outter: " + SwingUtilities.convertPoint(label.getParent(), new Point(0, 0), outter));
                System.out.println("label to frame: " + SwingUtilities.convertPoint(label, new Point(0, 0), frame));
                System.out.println("label.getParent to frame: " + SwingUtilities.convertPoint(label.getParent(), new Point(0, 0), frame));
                System.out.println("outter to label: " + SwingUtilities.convertPoint(outter, new Point(0, 0), label));
                System.out.println("label to below: " + SwingUtilities.convertPoint(label, new Point(0, 0), below));
                System.out.println("below to label: " + SwingUtilities.convertPoint(below, new Point(0, 0), label));
            }
        });
    }        
}

Which generates (on my system) the following output

lable.location: java.awt.Point[x=65,y=62]
label to inner: java.awt.Point[x=65,y=62]
label to outter: java.awt.Point[x=76,y=73]
label.parent to inner: java.awt.Point[x=0,y=0]
label.parent to outter: java.awt.Point[x=11,y=11]
label to frame: java.awt.Point[x=76,y=95]
label.getParent to frame: java.awt.Point[x=11,y=33]
outter to label: java.awt.Point[x=-76,y=-73]
label to below: java.awt.Point[x=76,y=-89]
below to label: java.awt.Point[x=-76,y=89]

If I pass the label as the source component, I get relative positions based upon the relationship between the label and the component whose coordinate space I'm trying to convert to. If I pass the label's parent, I'm using the parent coordinate space instead, which is bound to produce an incorrect result

If you look at the relationship between label and below it makes sense to that you would get negative results, as label is above and to the right of below

SwingUtilities.convertPoint() returns negative values

2 Answers2