用菜单实现，打开一个图片文件，并把该图片在窗体中显示出来。

package GUI;

import javax.swing.;
import javax.swing.filechooser.FileFilter;
import javax.swing.filechooser.FileNameExtensionFilter;
import java.awt.;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.io.File;
import java.io.IOException;
import java.net.URI;


public class MenuTest extends JFrame {


    public JPanel jp;
    public JMenuBar jMenuBar;
    public JMenu menu_File, menu_Edit, menu_View, menu_About;
    public JMenuItem menuItem_Open, menuItem_Exit1, menuItem_Exit2,
                     menuItem_Exit3, menuItem_Exit4, menuItem_New,
                     menuItem_Cut, menuItem_Copy, menuItem_MyBlog;
    public JLabel jLabel_img;

    public MenuTest(){

        this.setTitle("菜单");
        this.setSize(500, 500);
        this.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
        this.setLocationRelativeTo(null);
        this.setResizable(false);

        jp = new JPanel(new FlowLayout());

        jMenuBar = new JMenuBar();

        menu_File = new JMenu("文件");
        menu_Edit = new JMenu("编辑");
        menu_View = new JMenu("视图");
        menu_About = new JMenu("关于");

        jMenuBar.add(menu_File);
        jMenuBar.add(menu_Edit);
        jMenuBar.add(menu_View);
        jMenuBar.add(menu_About);

        //-=-=-=-=-=-=-文件-=-=-=-=-=-=-
        menuItem_New = new JMenuItem("新建");
        menuItem_Open = new JMenuItem("打开");
        menuItem_Exit1 = new JMenuItem("退出");

        menu_File.add(menuItem_New);
        menu_File.add(menuItem_Open);
        menu_File.addSeparator();
        menu_File.add(menuItem_Exit1);


        //-=-=-=-=-=-=-编辑-=-=-=-=-=-=-
        menuItem_Copy = new JMenuItem("复制");
        menuItem_Cut = new JMenuItem("裁剪");
        menuItem_Exit2 = new JMenuItem("退出");

        menu_Edit.add(menuItem_Copy);
        menu_Edit.add(menuItem_Cut);
        menu_Edit.addSeparator();
        menu_Edit.add(menuItem_Exit2);


        //-=-=-=-=-=-=-视图-=-=-=-=-=-=-
        menuItem_Exit3 = new JMenuItem("退出");
        menu_View.add(menuItem_Exit3);


        //-=-=-=-=-=-=-关于-=-=-=-=-=-=-
        menuItem_MyBlog = new JMenuItem("银月のBlog");
        menuItem_Exit4 = new JMenuItem("退出");

        menu_About.add(menuItem_MyBlog);
        menu_About.addSeparator();
        menu_About.add(menuItem_Exit4);

        ActL actL = new ActL();

        menuItem_Open.addActionListener(actL);
        menuItem_Exit1.addActionListener(actL);
        menuItem_Exit2.addActionListener(actL);
        menuItem_Exit3.addActionListener(actL);
        menuItem_Exit4.addActionListener(actL);
        menuItem_MyBlog.addActionListener(actL);

        jLabel_img = new JLabel("假装我是一张图片");

        jp.add(jLabel_img);

        this.setJMenuBar(jMenuBar);
        this.setContentPane(jp);
        this.setVisible(true);

    }

    class ActL implements ActionListener{

        @Override
        public void actionPerformed(ActionEvent actionEvent) {
            String m = actionEvent.getActionCommand();
            if(m.equals("退出")) {
                System.exit(0);
            } else if(m.equals("打开")) {
                int i = fileChooser.showOpenDialog(getContentPane());

                //↓判断用户单击的是否为"打开"按钮
                if (i == JFileChooser.APPROVE_OPTION) {

                    File selectedFile = fileChooser.getSelectedFile();
                    Image img = Toolkit.getDefaultToolkit().getImage(selectedFile.getAbsolutePath());
                    //↓按尺寸缩放并将Image转换为ImageIcon
                    ImageIcon imgIco = new ImageIcon(img.getScaledInstance(500,400,img.SCALE_SMOOTH));
                    jLabel_img.setIcon(imgIco);
                    jLabel_img.setText(null);
                }
            } else if(m.equals("银月のBlog")) {
                URI uri=java.net.URI.create("https://i.loli.link");
                Desktop dp=java.awt.Desktop.getDesktop();
                //↓获取系统默认浏览器打开链接
                if(dp.isSupported(java.awt.Desktop.Action.BROWSE)){
                    try {
                        dp.browse(uri);
                    } catch (IOException e) {
                        e.printStackTrace();
                    }
                }

            } else {
                System.out.println(m);
            }
        }

        JFileChooser fileChooser;
        {
            fileChooser = new JFileChooser();
            FileFilter filter = new FileNameExtensionFilter
                    ("图像文件（JPG/PNG/GIF）", "JPG", "JPEG", "GIF", "PNG");
            fileChooser.setFileFilter(filter);
        }
    }

    public static void main (String[] args){
        new MenuTest();
    }



`}
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