Background image in java

Question

hi,

i'm trying to put an image as a background of my interface in java , i tried to write a class that does that and using it , but is there a simpler way to do that .

here 's the code i used:

import java.awt.BorderLayout;
import java.awt.Dimension;
import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;
import javax.swing.BorderFactory;
import javax.swing.Icon;
import javax.swing.ImageIcon;
import javax.swing.JComponent;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTextArea;

public class BackgroundImagePanelExample {

    // Set up contraints so that the user supplied component and the
    // background image label overlap and resize identically
    private static final GridBagConstraints gbc;

    static {
        gbc = new GridBagConstraints();
        gbc.gridx = 0;
        gbc.gridy = 0;
        gbc.weightx = 1.0;
        gbc.weighty = 1.0;
        gbc.fill = GridBagConstraints.BOTH;
        gbc.anchor = GridBagConstraints.NORTHWEST;
    }

    /**
     * Wraps a Swing JComponent in a background image. Simply invokes the overloded
     * variant with Top/Leading alignment for background image.
     *
     * @param component - to wrap in the a background image
     * @param backgroundIcon - the background image (Icon)
     * @return the wrapping JPanel
     */
    public static JPanel wrapInBackgroundImage(JComponent component,
        Icon backgroundIcon) {
        return wrapInBackgroundImage(
            component,
            backgroundIcon,
            JLabel.TOP,
            JLabel.LEADING);
    }

    /**
     * Wraps a Swing JComponent in a background image. The vertical and horizontal
     * alignment of background image can be specified using the alignment
     * contants from JLabel.
     *
     * @param component - to wrap in the a background image
     * @param backgroundIcon - the background image (Icon)
     * @param verticalAlignment - vertical alignment. See contants in JLabel.
     * @param horizontalAlignment - horizontal alignment. See contants in JLabel.
     * @return the wrapping JPanel
     */
    public static JPanel wrapInBackgroundImage(JComponent component,
        Icon backgroundIcon,
        int verticalAlignment,
        int horizontalAlignment) {

        // make the passed in swing component transparent
        component.setOpaque(false);

        // create wrapper JPanel
        JPanel backgroundPanel = new JPanel(new GridBagLayout());

        // add the passed in swing component first to ensure that it is in front
        backgroundPanel.add(component, gbc);

        // create a label to paint the background image
        JLabel backgroundImage = new JLabel(backgroundIcon);

        // set minimum and preferred sizes so that the size of the image
        // does not affect the layout size
        backgroundImage.setPreferredSize(new Dimension(1, 1));
        backgroundImage.setMinimumSize(new Dimension(1, 1));

        // align the image as specified.
        backgroundImage.setVerticalAlignment(verticalAlignment);
        backgroundImage.setHorizontalAlignment(horizontalAlignment);

        // add the background label
        backgroundPanel.add(backgroundImage, gbc);

        // return the wrapper
        return backgroundPanel;
    }

    public static void main(String[] args) {
        JFrame frame = new JFrame("Background Image Panel Example");

        // Create some GUI
        JPanel foregroundPanel = new JPanel(new BorderLayout(10, 10));
        foregroundPanel.setBorder(
            BorderFactory.createEmptyBorder(10, 10, 10, 10));
        foregroundPanel.setOpaque(false);

        foregroundPanel.add(new JLabel("Comment:"), BorderLayout.NORTH);
        foregroundPanel.add(new JScrollPane(new JTextArea(3, 10)),
            BorderLayout.CENTER);
        foregroundPanel.add(
            new JLabel(
            "Please enter your comments in text box above."
            + " HTML syntax is allowed."), BorderLayout.SOUTH);

        frame.setContentPane(wrapInBackgroundImage(foregroundPanel,
            new ImageIcon(
            BackgroundImagePanelExample.class.getResource("backgd.jpg"))));

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

thanks

Answer 1

I dont actually see what are you asking. If you are asking, whether there is simpler way to build swing apps - than answer is YES. Use NetBeans IDE with Swing builder which produces very reasonable generated code and lets you edit whole bunch of componenets. Hand written Swing is more often "broken" than generated code from NetBeans, and much much more time consuming ...

Answer 2

I'm guessing you're getting java.lang.NullPointerException because backgd.jpg can't be found by getResource(). You might be able to put the image file alongside the source file and rebuild the project. Alternatively, you can load it from the file system as a temporary measure while you sort things out.

frame.setContentPane(wrapInBackgroundImage(
    foregroundPanel, new ImageIcon("image.jpg")));

Answer 3

import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Image;

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

public class ImageTest {

  public static void main(String[] args) {
    ImagePanel panel = new ImagePanel(new ImageIcon("images/background.png").getImage());

    JFrame frame = new JFrame();
    frame.getContentPane().add(panel);
    frame.pack();
    frame.setVisible(true);
  }
}

class ImagePanel extends JPanel {

  private Image img;

  public ImagePanel(String img) {
    this(new ImageIcon(img).getImage());
  }

  public ImagePanel(Image img) {
    this.img = img;
    Dimension size = new Dimension(img.getWidth(null), img.getHeight(null));
    setPreferredSize(size);
    setMinimumSize(size);
    setMaximumSize(size);
    setSize(size);
    setLayout(null);
  }

  public void paintComponent(Graphics g) {
    g.drawImage(img, 0, 0, null);
  }

}