Java基础之处理事件——使窗口处理自己的事件（Skethcer 1 handing its own closing event）

控制台程序。

为表示事件的常量使用标识符可以直接启用组件对象的特定事件组。调用组件的enableEvent()方法，并把想要启用事件的标识符传送为参数，但这只在不使用监视器的情况下有效。注册监听器会自动启用监听器想要监听的事件，所以不需要调用enableEvent()方法。只有当希望对象能处理自己的某些事件时，才调用enableEvent()方法，但使用监听器可以达到相同的效果。

使用监听器对象是处理事件的首选方式，因为更容易直接启用对象的事件，代码也更简洁。

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

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

    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
    enableEvents(WINDOW_EVENT_MASK);                                   // Enable window events
  }

  // Handle window events
  protected void processWindowEvent(WindowEvent e) {
    if (e.getID() == WindowEvent.WINDOW_CLOSING) {
      dispose();                                                       // Release resources
      System.exit(0);                                                  // Exit the program
    }
    super.processWindowEvent(e);                                       // Pass on the event
  }

  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
}