将JLabel移动到Front

Question

I am placing two images. One is supposed to be the background picture and the other one a picture of a stick-figure. I'd like to get the stick figure in front of the background. I can accomplish this by inserting the code to put the background picture after the code to display the stick figure. I was wondering if there was anyway to accomplish the same thing, by inserting the stick figure code after the background code, so I could keep placing new JLabels on top of the background.

The code that works:

    guy.setBounds(0,0,100,100);
    panel.add(guy);

    backgroundPic.setBounds(0,0,550,550);
    panel.add(backgroundPic);

    setVisible(true);

The code that I'd like to work:

    backgroundPic.setBounds(0,0,550,550);
    panel.add(backgroundPic);

    guy.setBounds(0,0,100,100);
    panel.add(guy);


    setVisible(true);

Answer 1

If you are only worrying about one background image, then I would suggest to extend JPanel, override paintComponent and paint the background image.

If you have to care about the Z-order of several components, then JLayeredPane is your best alternative.

Here is a small snippet showing the first option:

import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Image;
import java.awt.Point;
import java.net.MalformedURLException;
import java.net.URL;

import javax.swing.ImageIcon;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;

public class Test2 {
    private static class PanelWithBackground extends JPanel {

        private Image backgroundImage;
        private Point backgroundLocation = new Point();

        @Override
        protected void paintComponent(Graphics g) {
            super.paintComponent(g);
            if (getBackgroundImage() != null) {
                g.drawImage(getBackgroundImage(), backgroundLocation.x, backgroundLocation.y, this);
            }
        }

        public Image getBackgroundImage() {
            return backgroundImage;
        }

        public void setBackgroundImage(Image backgroundImage) {
            this.backgroundImage = backgroundImage;
            repaint();
        }

        public Point getBackgroundLocation() {
            return backgroundLocation;
        }

        public void setBackgroundLocation(Point backgroundLocation) {
            this.backgroundLocation = backgroundLocation;
            repaint();
        }
    }

    protected static void initUI() throws MalformedURLException {
        JFrame frame = new JFrame("test");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        PanelWithBackground panelWithBackground = new PanelWithBackground();
        panelWithBackground.setLayout(null);
        panelWithBackground.setBackgroundImage(new ImageIcon(new URL(
                "http://2.bp.blogspot.com/-PqKuKt5mRmc/Tvi-K-4FVVI/AAAAAAAACKg/YwzkME5gGvk/s1600/black+background.jpg")).getImage());
        JLabel guy = new JLabel(new ImageIcon(new URL(
                "http://www.clipproject.info/Cliparts_Free/Menschen_Free/Clipart-Cartoon-Design-04.gif")));
        // Next 2 lines should rather be performed by a LayoutManager
        panelWithBackground.setPreferredSize(new Dimension(1024, 768));
        guy.setBounds(50, 200, guy.getPreferredSize().width, guy.getPreferredSize().height);

        panelWithBackground.add(guy);
        frame.add(panelWithBackground);
        frame.pack();
        frame.setVisible(true);
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {

            @Override
            public void run() {
                try {
                    initUI();
                } catch (MalformedURLException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
            }
        });
    }
}

Answer 2

You can use the Z order, to indicate the order the components should be rendered:

java.awt.Container.getComponentZOrder(Component)

According documentation:

Returns the z-order index of the component inside the container. The higher a component is in the z-order hierarchy, the lower its index. The component with the lowest z-order index is painted last, above all other child components.

Parameters: comp the component being queried

Returns: the z-order index of the component; otherwise returns -1 if the component is null or doesn't belong to the container

Answer 3

I wont claim to be a java expert nor will i claim this is correct, just a guess, but try and remove the

.setBounds()

and if that has no effect, try using

.setSize()

best of luck :)