swing设置背景图片

A. java窗体如何添加背景图片

B. java swing换背景图片

//回答完毕，采纳即可

importjava.awt.BorderLayout;
importjava.awt.Graphics;
importjava.awt.Image;
importjava.awt.event.ActionEvent;
importjava.awt.event.ActionListener;
importjava.awt.event.WindowAdapter;
importjava.awt.event.WindowEvent;
importjava.io.IOException;

importjavax.imageio.ImageIO;
importjavax.swing.BorderFactory;
importjavax.swing.JButton;
importjavax.swing.JComboBox;
importjavax.swing.JDialog;
importjavax.swing.JFrame;
importjavax.swing.JPanel;

publicclassBarextendsJPanel
{
	=1L;

	privateJButtonopen;

	privatestaticfinalintW=300;

	privatestaticfinalintH=300;

	publicBar()
	{
		super(newBorderLayout());

		JPanelpanel=newJPanel();
		open=newJButton("打开");
		open.addActionListener(newActionListener()
		{
			@Override
			publicvoidactionPerformed(ActionEvente)
			{
				JDialogdialog=newJDialog();
				dialog.setTitle("设置背景图");
				dialog.setSize(160,60);
				dialog.setModal(true);
				dialog.setLocationRelativeTo(Bar.this);
				dialog.setDefaultCloseOperation(JDialog.DISPOSE_ON_CLOSE);
				finalJComboBoxcomboBox=newJComboBox(newString[]{"图片a","图片b"});
				dialog.addWindowListener(newWindowAdapter()
				{
					@Override
					publicvoidwindowClosing(WindowEvente)
					{
						try
						{
							intindex=comboBox.getSelectedIndex();
							switch(index)
							{
								case0:
									img=ImageIO.read(Bar.class.getResource("a.jpg"));
									Bar.this.repaint();
									break;
								case1:
									img=ImageIO.read(Bar.class.getResource("layout.png"));
									Bar.this.repaint();
									break;
								default:
									break;
							}
						}
						catch(IOExceptione1)
						{
							e1.printStackTrace();
						}
					}
				});
				dialog.add(comboBox);
				dialog.setVisible(true);
			}
		});
		panel.add(open);
		add(panel,BorderLayout.PAGE_START);
		setBorder(BorderFactory.createEmptyBorder(20,20,20,20));
	}

	Imageimg=null;

	@Override
	publicvoidpaint(Graphicsg)
	{
		super.paint(g);
		g.clearRect(0,0,W,H);
		g.drawImage(img,0,0,null);
		g.dispose();
	}

	()
	{
		JFrameframe=newJFrame("bar");
		frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		Barb=newBar();
		b.setOpaque(true);
		frame.setContentPane(b);
		frame.setSize(W,H);
		frame.setResizable(false);
		frame.setLocationRelativeTo(null);
		frame.setVisible(true);
	}

	publicstaticvoidmain(String[]args)
	{
		javax.swing.SwingUtilities.invokeLater(newRunnable()
		{
			publicvoidrun()
			{
				createAndShowGUI();
			}
		});
	}
}

//重写JPanel的这个方法就可以了
@Override
publicvoidpaintComponent(Graphicsgs){
Graphics2Dg=(Graphics2D)gs;
super.paintComponent(g);
//画背景图片
Imageimage=Toolkit.getDefaultToolkit().getImage(getClass().getResource(imgPath));
g.drawImage(image,0,0,width,height,this);
}

packagetest;

importjava.awt.Graphics;
importjava.awt.Image;
importjava.net.URL;

importjavax.swing.ImageIcon;
importjavax.swing.JFrame;
importjavax.swing.JPanel;

//为窗口添加背景图片
publicclassJFrameBackground{

	privateJFrameframe=newJFrame("带背景图片的JFrame");
	privateJPanelimagePanel;
	privateImageIconbackgroundimg;

	publicJFrameBackground(){

		imagePanel=newJPanel(){
			@Override
			protectedvoidpaintComponent(Graphicsg){
				super.paintComponent(g);
				URLlocation=this.getClass().getResource("grapes.gif");
				backgroundimg=newImageIcon(location);
				Imageimg=backgroundimg.getImage();
				g.drawImage(img,0,0,backgroundimg.getIconWidth(),
						backgroundimg.getIconHeight(),
						backgroundimg.getImageObserver());
				frame.setSize(backgroundimg.getIconWidth(),
						backgroundimg.getIconHeight());
			}

		};

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

	publicstaticvoidmain(String[]args){
		newJFrameBackground();
	}
}