为Java的JLayeredPane组件添加窗口背景图片

用JLayeredPane实现在不影响窗口组件布局的情况下，添加一个背景图片：

、

调整窗口大小后：

package com.han;    import java.awt.BorderLayout;  import java.awt.Container;  import java.awt.Dimension;  import java.awt.Image;  import java.awt.Point;  import java.awt.Rectangle;  import java.awt.Toolkit;  import java.awt.event.ComponentAdapter;  import java.awt.event.ComponentEvent;    import javax.swing.BorderFactory;  import javax.swing.ImageIcon;  import javax.swing.JButton;  import javax.swing.JFrame;  import javax.swing.JLabel;  import javax.swing.JLayeredPane;  import javax.swing.JPanel;    /**   * The JLayeredPane has no layout manager by default, so you have to use    * setBounds() for each component in it. However, you can still assign a layout   * manager to the layered pane.   * 
   * Many programs use intermediate containers (such as panels) and their layout    * managers to lay out components on the same layer, but use absolute    * positioning to lay out components on different layers.   * 
  
   * We can use frame.pack() or frame.setSize() whatever its layout method is    * (use a layout manager or not).   * 
  
   * In fact, if we hesitate to use component.setPreferredSize() or    * component.setSize(), we first see the layout method employed to layout this    * component. If it has a layout manager, we use component.setPreferredSize();    * else (no layout manager), we use component.setBounds().   * 
  
   * Concerning the JLayeredPane, the depth is higher, the component is on   * the top (of course, there are some depth conventions, like DEFAULT_LAYER,    * PALETTE_LAYER, ...). Within its depth, the position number is 0, top-most;    * -1, bottom-most; 0, 1, 2, 3, ... from top to bottom.   *    * @author HAN   *   */  @SuppressWarnings("serial")  public class JLayeredPane_1 extends JFrame {     public JLayeredPane_1() {    // TODO Auto-generated constructor stub    Container container = getContentPane();      final JLayeredPane layeredPane = new JLayeredPane();  //  layeredPane.setBorder(BorderFactory.createTitledBorder(null,   //    "layeredPane", TitledBorder.LEADING, TitledBorder.TOP,   //    new Font(null, Font.BOLD + Font.ITALIC, 14), Color.RED));    layeredPane.setBorder(BorderFactory.createTitledBorder("" +      "layeredPane" +      ""));    Dimension dimension = new Dimension(300, 310);    layeredPane.setPreferredSize(dimension);        final JPanel panelBg = new JPanel();    final Image imageBg = Toolkit.getDefaultToolkit()      .getImage(this.getClass().getResource("/images/Lighthouse.jpg"));    ImageIcon imageIcon = new ImageIcon(imageBg.getScaledInstance      (dimension.width, dimension.height, Image.SCALE_FAST));    final JLabel bg = new JLabel(imageIcon);    final Point origin = new Point(10, 30);    final Rectangle rectangle = new Rectangle(origin, dimension);    panelBg.setBounds(rectangle);    panelBg.add(bg);        final JPanel panelContent = new JPanel();    JButton button = new JButton("button 1");    JButton button2 = new JButton("button 2");      JButton button3 = new JButton("button 3");     panelContent.setBounds(rectangle);    panelContent.setOpaque(false); // 设置为透明    panelContent.add(button);    panelContent.add(button2);    panelContent.add(button3);        layeredPane.add(panelBg, new Integer(0)); // the same to layeredPane.add(panelBg);    layeredPane.add(panelContent, new Integer(1));        container.add(layeredPane, BorderLayout.CENTER);        addComponentListener(new ComponentAdapter() {     public void componentResized(ComponentEvent e) {  //    System.out.println(layeredPane.getSize()); //此处必须用getSize()而不是用getPreferredSize()  //    System.out.println(layeredPane.getPreferredSize());      Dimension dimensionNew = layeredPane.getSize();      Rectangle rectangleNew = new Rectangle(origin, dimensionNew);      panelBg.setBounds(rectangleNew);      panelContent.setBounds(rectangleNew);      bg.setIcon(new ImageIcon(imageBg.getScaledInstance      (dimensionNew.width, dimensionNew.height, Image.SCALE_FAST)));     }    });   }     /**    * @param args    * @throws Exception     */   public static void main(String[] args) {    // TODO Auto-generated method stub    JLayeredPane_1 frame = new JLayeredPane_1();    frame.pack();    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);    frame.setVisible(true);   }    }