swing快速入门（二十五）

注释很详细，直接上代码

新增内容

1.ImageIO.write读取并显示图片

2.ImageIO.writeImageIO.write读取并保存图片

package swing21_30;

import javax.imageio.ImageIO;
import java.awt.*;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;
import java.awt.image.BufferedImage;
import java.io.File;
import java.io.IOException;

public class swing_test_23 {

    private Frame frame=new Frame("swing_test_23");
    MenuBar menuBar=new MenuBar();
    Menu menu=new Menu("文件");
    MenuItem open=new MenuItem("打开");

    MenuItem save=new MenuItem("另存为");

    //声明BufferedImage对象,记录本地图片
    BufferedImage image;

    private class MyCanvas extends Canvas{
        @Override
        public void paint(Graphics g){
        g.drawImage(image,0,0,null);
        }
    }

    MyCanvas drawArea=new MyCanvas();

    public void init() throws Exception{

        //组装视图
        open.addActionListener(e -> {

            //打开文件
            FileDialog fileDialog=new FileDialog(frame,"打开图片",FileDialog.LOAD);
            fileDialog.setVisible(true);

            //获取用户选择的图片路径以及名称
            String dir=fileDialog.getDirectory();

            String filename=fileDialog.getFile();

            try{
                image= ImageIO.read(new File(dir+filename));
                drawArea.repaint();
            } catch (IOException ex) {
                throw new RuntimeException(ex);
            }

        });

        save.addActionListener(e->{

            //展示一个文件对话框
            FileDialog fileDialog=new FileDialog(frame,"保存图片",FileDialog.SAVE);
            fileDialog.setVisible(true);

            //获取用户设置的保存路径和文件名称
            String dir=fileDialog.getDirectory();
            String filename=fileDialog.getFile();

            try{
                ImageIO.write(image,"JPEG",new File(dir,filename));
            }catch (IOException ex){
                ex.printStackTrace();
            }

        });

        // 设置窗口大小
        frame.setBounds(200,200,740,508);

        // 显示窗口
        frame.setVisible(true);

        // 关闭窗口时退出程序
        frame.addWindowListener(new WindowAdapter() {
            @Override
            public void windowClosing(WindowEvent e) {
                System.exit(0);
            }
        });

        // 菜单栏
        menu.add(open);
        menu.add(save);

        menuBar.add(menu);

        //把菜单条目添加到菜单栏中
        frame.setMenuBar(menuBar);
        frame.add(drawArea);//把画布添加到窗口中

        frame.setBounds(200,200,740,508);

        frame.setVisible(true);
    }

    public static void main(String[] args) {
        //直接运行init
        try {
            new swing_test_23().init();
        } catch (Exception e) {
            throw new RuntimeException(e);
        }

    }
}

运行效果