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();
}

}