一个浏览图片程序

import Javax.swing.*;
import java.awt.Graphics;
import java.awt.*;
import java.awt.event.*;

public class ImageViewer extends JFrame{

Image imageFirst;//初始图像
ImagePanel panel=new ImagePanel();//用来显示图像的panel

JMenuBar jmb=new JMenuBar();

JMenu file=new JMenu("File");
JMenu modify=new JMenu("Modify");

JMenuItem open=new JMenuItem("open");
JMenuItem exit=new JMenuItem("exit");

ButtonGroup bg=new ButtonGroup();
JRadioButtonMenuItem rate1=new JRadioButtonMenuItem("to 50%");//这三个菜单项
JRadioButtonMenuItem rate2=new JRadioButtonMenuItem("to 100%");//用来改变图像
JRadioButtonMenuItem rate3=new JRadioButtonMenuItem("to 200%");//显示的大小

JToolBar toolbar=new JToolBar();//只有一个button简单的toolbar
JButton button=new JButton("A JToolBar Contain A Jbutton");

ImageViewer(){

this.getContentPane().setLayout(null);

this.setBounds(200,200,500,400);
this.setResizable(false);
this.setTitle("ImageViewer");

imageFirst=java.awt.Toolkit.getDefaultToolkit().getImage("images/opean.gif");
panel.setImage(imageFirst);

jmb.add(file);
jmb.add(modify);

open.addActionListener(new OpenAction());
file.add(open);
file.add(exit);

bg.add(rate1); bg.add(rate2); bg.add(rate3);
modify.add(rate1);
modify.add(rate2); rate2.setSelected(true);
modify.add(rate3);

rate1.addItemListener(new ItemListener(){
public void itemStateChanged(ItemEvent e){
if(rate1.isSelected()==true){
panel.setRate(0.5);
System.out.println("rate1 been selected!");
panel.repaint();
}
}
});

rate2.addItemListener(new ItemListener(){
public void itemStateChanged(ItemEvent e){
if(rate2.isSelected()==true){
panel.setRate(1);
System.out.println("rate2 been selected!");
panel.repaint();
}
}
});

rate3.addItemListener(new ItemListener(){
public void itemStateChanged(ItemEvent e){
if(rate3.isSelected()==true){
panel.setRate(2);
System.out.println("rate3 been selected!");
panel.repaint();
}
}
});
exit.addActionListener(new ActionListener(){
public void actionPerformed(ActionEvent e){
System.exit(0);
}});

this.setJMenuBar(jmb);

panel.setBounds(0,30,this.getWidth(),this.getHeight()-60);
this.getContentPane().add(panel);

button.addActionListener(new ActionListener(){
public void actionPerformed(ActionEvent e){
JOptionPane.showMessageDialog(null,this);
}
});
toolbar.add(button);
toolbar.setLayout(new GridLayout());
toolbar.setBackground(Color.blue);
toolbar.setBounds(0,0,500,30);
this.getContentPane().add(toolbar);
}//SwingDemo1

//主方法
public static void main(String argv[]){

JFrame.setDefaultLookAndFeelDecorated(true);
ImageViewer app=new ImageViewer();
app.setVisible(true);

app.repaint();
}

//内部类　菜单项ｏｐｅａｎ处理事件
class OpenAction implements ActionListener{
public void actionPerformed(ActionEvent e){

JFileChooser fc = new JFileChooser();
int returnVal = fc.showDialog(new ImageViewer(), "Open file");
String file = fc.getSelectedFile().getPath();
panel.setImage(file);
panel.repaint();

System.out.println("open file action performed");
}
}

}

//外部类　　Ｐａｎｅｌ用来显示ｉｍａｇｅ
class ImagePanel extends JPanel
{
private Image image;
private double rate=1;

Dimension offDimension;
Image offImage;
Graphics offGraphics;

ImagePanel(){
this.setBackground(Color.blue);
}

public void update(Graphics g){
if(image!=null){
g.drawImage(image,0,0,
(int)(this.getWidth()*rate/2),(int)(this.getHeight()*rate/2),
this.getRootPane());
}
else
{g.setColor(Color.red);
g.fillRect(0,0,(int)(250*rate),(int)(200*rate));
}
}
public void paint(Graphics g){
update(g);
}

public void setImage(Image image){
this.image=image;
}

public void setRate(double rate){
this.rate=rate;
}

public void setImage(String s){
this.image=java.awt.Toolkit.getDefaultToolkit().getImage(s);
}
}