Java基础之创建窗口——向窗口中添加菜单（Sketcher）

控制台程序。

JMenuBar对象表示放在窗口顶部的菜单栏。可以为JMenuBar对象添加JMenu或JMenuItem对象，它们都显示在菜单栏上。JMenu对象是带有标签的菜单，单击就可以显示一列菜单项。JMenuItem对象表示菜单中带有标签的菜单项，单击就会执行某个程序动作。

 // Main window for the Sketcher application
 import javax.swing.*;
 import static java.awt.event.InputEvent.*;                             // For modifier constants

 @SuppressWarnings("serial")
 public class SketcherFrame extends JFrame {
   // Constructor
   public SketcherFrame(String title) {
     setTitle(title);                                                   // Set the window title
     setDefaultCloseOperation(EXIT_ON_CLOSE);

     setJMenuBar(menuBar);                                              // Add the menu bar to the window

     JMenu fileMenu = new JMenu("File");                                // Create File menu
     JMenu elementMenu = new JMenu("Elements");                         // Create Elements menu
     fileMenu.setMnemonic('F');                                         // Create shortcut
     elementMenu.setMnemonic('E');                                      // Create shortcut

     // Construct the file drop-down menu
     newItem = fileMenu.add("New");                                      // Add New item
     openItem = fileMenu.add("Open");                                    // Add Open item
     closeItem = fileMenu.add("Close");                                  // Add Close item
     fileMenu.addSeparator();                                            // Add separator
     saveItem = fileMenu.add("Save");                                    // Add Save item
     saveAsItem = fileMenu.add("Save As...");                            // Add Save As item
     fileMenu.addSeparator();                                            // Add separator
     printItem = fileMenu.add("Print");                                  // Add Print item

     // Add File menu accelerators
     newItem.setAccelerator(KeyStroke.getKeyStroke('N',CTRL_DOWN_MASK ));
     openItem.setAccelerator(KeyStroke.getKeyStroke('O', CTRL_DOWN_MASK));
     saveItem.setAccelerator(KeyStroke.getKeyStroke('S', CTRL_DOWN_MASK));
     printItem.setAccelerator(KeyStroke.getKeyStroke('P', CTRL_DOWN_MASK));

     // Construct the Element drop-down menu
     elementMenu.add(lineItem = new JRadioButtonMenuItem("Line", true));
     elementMenu.add(rectangleItem = new JRadioButtonMenuItem("Rectangle", false));
     elementMenu.add(circleItem = new JRadioButtonMenuItem("Circle", false));
     elementMenu.add(curveItem = new JRadioButtonMenuItem("Curve", false));
     ButtonGroup types = new ButtonGroup();
     types.add(lineItem);
     types.add(rectangleItem);
     types.add(circleItem);
     types.add(curveItem);

     // Add element type accelerators
     lineItem.setAccelerator(KeyStroke.getKeyStroke('L', CTRL_DOWN_MASK));
     rectangleItem.setAccelerator(KeyStroke.getKeyStroke('E', CTRL_DOWN_MASK));
     circleItem.setAccelerator(KeyStroke.getKeyStroke('I', CTRL_DOWN_MASK));
     curveItem.setAccelerator(KeyStroke.getKeyStroke('V', CTRL_DOWN_MASK));

     elementMenu.addSeparator();
     JMenu colorMenu = new JMenu("Color");                              // Color submenu
     elementMenu.add(colorMenu);                                        // Add the submenu
     colorMenu.add(redItem = new JCheckBoxMenuItem("Red", false));
     colorMenu.add(yellowItem = new JCheckBoxMenuItem("Yellow", false));
     colorMenu.add(greenItem = new JCheckBoxMenuItem("Green", false));
     colorMenu.add(blueItem = new JCheckBoxMenuItem("Blue", true));

     // Add element color accelerators
     redItem.setAccelerator(KeyStroke.getKeyStroke('R', CTRL_DOWN_MASK));
     yellowItem.setAccelerator(KeyStroke.getKeyStroke('Y', CTRL_DOWN_MASK));
     greenItem.setAccelerator(KeyStroke.getKeyStroke('G', CTRL_DOWN_MASK));
     blueItem.setAccelerator(KeyStroke.getKeyStroke('B', CTRL_DOWN_MASK));

     menuBar.add(fileMenu);                                             // Add the file menu
     menuBar.add(elementMenu);                                          // Add the element menu
   }

   private JMenuBar menuBar = new JMenuBar();                           // Window menu bar

   // File menu items
   private JMenuItem newItem,  openItem,   closeItem,
                     saveItem, saveAsItem, printItem;

   // Element menu items
   private JRadioButtonMenuItem lineItem,  rectangleItem, circleItem,   // Types
                                curveItem, textItem;
   private JCheckBoxMenuItem    redItem,   yellowItem,                  // Colors
                                greenItem, blueItem ;
 }

 // Sketching application
 import javax.swing.*;
 import java.awt.*;

 import javax.swing.SwingUtilities;

 public class Sketcher {
   public static void main(String[] args) {
     SwingUtilities.invokeLater(new Runnable() {
             public void run() {
                 createWindow();
             }
         });
   }

   public static void createWindow(){
     window = new SketcherFrame("Sketcher");                            // Create the app window
     Toolkit theKit = window.getToolkit();                              // Get the window toolkit
     Dimension wndSize = theKit.getScreenSize();                        // Get screen size

     // Set the position to screen center & size to half screen size
     window.setSize(wndSize.width/2, wndSize.height/2);                 // Set window size
     window.setLocationRelativeTo(null);                                // Center window
     window.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

     window.setVisible(true);
   }

   private static SketcherFrame window;                                 // The application window
 }