Java基础之处理事件——使用动作Action（Sketcher 6 using Action objects）

控制台程序。

动作Action是任何实现了javax.swing.Action接口的类的对象。这个接口声明了操作Action对象的方法，例如，存储与动作相关的属性、启用和禁用动作。Action接口扩展了ActionListener接口，所以Action对象既是监听器，也是动作。

一些Swing组件，包括JMenu和JToolBar类型的组件，都有add()方法，可以接受Action类型的参数。当使用add()方法把Action对象添加到JMenu对象中，add()方法就会创建类型自动正确的组件。如果把Action对象添加到JMenu对象中，add()方法就会创建并返回JmentItem对象。另一方面，当把相同的Action对象添加到Action对象中时，会创建并返回JButton类型的对象。这意味着可以给菜单和工具栏添加相同的Action对象，因为Action对象是自己的监听器，所以可以自动获得由相同动作支持的菜单项和工具栏按钮。

下面使用Action重建SketcherFrame类：

 // Frame for the Sketcher application
 import javax.swing.*;
 import java.awt.event.*;
 import java.awt.*;

 import static java.awt.event.InputEvent.*;
 import static java.awt.AWTEvent.*;
 import static java.awt.Color.*;
 import static Constants.SketcherConstants.*;

 @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
     setDefaultCloseOperation(EXIT_ON_CLOSE);                           // Default is exit the application

     createFileMenu();                                                  // Create the File menu
     createElementMenu();                                               // Create the element menu
     createColorMenu();                                                 // Create the element menu
   }

   // Create File menu item actions
   private void createFileMenuActions() {
     newAction = new FileAction("New", 'N', CTRL_DOWN_MASK);
     openAction = new FileAction("Open", 'O', CTRL_DOWN_MASK);
     closeAction = new FileAction("Close");
     saveAction = new FileAction("Save", 'S', CTRL_DOWN_MASK);
     saveAsAction = new FileAction("Save As...");
     printAction = new FileAction("Print", 'P', CTRL_DOWN_MASK);
     exitAction = new FileAction("Exit", 'X', CTRL_DOWN_MASK);

     // Initialize the array
     FileAction[] actions = {openAction, closeAction, saveAction, saveAsAction, printAction, exitAction};
     fileActions = actions;
   }

   // Create the File menu
   private void createFileMenu() {
     JMenu fileMenu = new JMenu("File");                                // Create File menu
     fileMenu.setMnemonic('F');                                         // Create shortcut
     createFileMenuActions();                                           // Create Actions for File menu item

     // Construct the file drop-down menu
     fileMenu.add(newAction);                                           // New Sketch menu item
     fileMenu.add(openAction);                                          // Open sketch menu item
     fileMenu.add(closeAction);                                         // Close sketch menu item
     fileMenu.addSeparator();                                           // Add separator
     fileMenu.add(saveAction);                                          // Save sketch to file
     fileMenu.add(saveAsAction);                                        // Save As menu item
     fileMenu.addSeparator();                                           // Add separator
     fileMenu.add(printAction);                                         // Print sketch menu item
     fileMenu.addSeparator();                                           // Add separator
     fileMenu.add(exitAction);                                          // Print sketch menu item
     menuBar.add(fileMenu);                                             // Add the file menu
   }

   // Create Element  menu actions
   private void createElementTypeActions() {
     lineAction = new TypeAction("Line", LINE, 'L', CTRL_DOWN_MASK);
     rectangleAction = new TypeAction("Rectangle", RECTANGLE, 'R', CTRL_DOWN_MASK);
     circleAction =  new TypeAction("Circle", CIRCLE,'C', CTRL_DOWN_MASK);
     curveAction = new TypeAction("Curve", CURVE,'U', CTRL_DOWN_MASK);

     // Initialize the array
     TypeAction[] actions = {lineAction, rectangleAction, circleAction, curveAction};
     typeActions = actions;
   }

   // Create the Element menu
   private void createElementMenu() {
     createElementTypeActions();
     elementMenu = new JMenu("Elements");                               // Create Elements menu
     elementMenu.setMnemonic('E');                                      // Create shortcut
     createRadioButtonDropDown(elementMenu, typeActions, lineAction);
     menuBar.add(elementMenu);                                          // Add the element menu
   }

   // Create Element  menu actions
   private void createElementColorActions() {
     redAction = new ColorAction("Red", RED, 'R', CTRL_DOWN_MASK|ALT_DOWN_MASK);
     yellowAction = new ColorAction("Yellow", YELLOW, 'Y', CTRL_DOWN_MASK|ALT_DOWN_MASK);
     greenAction = new ColorAction("Green", GREEN, 'G', CTRL_DOWN_MASK|ALT_DOWN_MASK);
     blueAction = new ColorAction("Blue", BLUE, 'B', CTRL_DOWN_MASK|ALT_DOWN_MASK);

     // Initialize the array
     ColorAction[] actions = {redAction, greenAction, blueAction, yellowAction};
     colorActions = actions;
   }

   // Create the Color menu
   private void createColorMenu() {
     createElementColorActions();
     colorMenu = new JMenu("Color");                                    // Create Elements menu
     colorMenu.setMnemonic('C');                                        // Create shortcut
     createRadioButtonDropDown(colorMenu, colorActions, blueAction);
     menuBar.add(colorMenu);                                            // Add the color menu
   }

   // Menu creation helper
   private void createRadioButtonDropDown(JMenu menu, Action[] actions, Action selected) {
     ButtonGroup group = new ButtonGroup();
     JRadioButtonMenuItem item = null;
     for(Action action : actions) {
       group.add(menu.add(item = new JRadioButtonMenuItem(action)));
       if(action == selected) {
         item.setSelected(true);                                        // This is default selected
       }
     }
   }

   // Inner class defining Action objects for File menu items
   class FileAction extends AbstractAction {
     // Create action with a name
     FileAction(String name) {
       super(name);
     }

     // Create action with a name and accelerator
     FileAction(String name, char ch, int modifiers) {
       super(name);
       putValue(ACCELERATOR_KEY, KeyStroke.getKeyStroke(ch, modifiers));

       // Now find the character to underline
       int index = name.toUpperCase().indexOf(ch);
       if(index != -1) {
         putValue(DISPLAYED_MNEMONIC_INDEX_KEY, index);
       }
     }

     // Event handler
     public void actionPerformed(ActionEvent e) {
       // You will add action code here eventually...
     }
   }

   // Inner class defining Action objects for Element type menu items
   class TypeAction extends AbstractAction {
     // Create action with just a name property
     TypeAction(String name, int typeID) {
       super(name);
       this.typeID = typeID;
     }

     // Create action with a name and an accelerator
     private TypeAction(String name,int typeID, char ch, int modifiers) {
       this(name, typeID);
       putValue(ACCELERATOR_KEY, KeyStroke.getKeyStroke(ch, modifiers));

       // Now find the character to underline
       int index = name.toUpperCase().indexOf(ch);
       if(index != -1) {
         putValue(DISPLAYED_MNEMONIC_INDEX_KEY, index);
       }
     }

     public void actionPerformed(ActionEvent e) {
       elementType = typeID;
     }

     private int typeID;
   }

   // Handles color menu items
   class ColorAction  extends AbstractAction {
     // Create an action with a name and a color
     public ColorAction(String name, Color color) {
       super(name);
       this.color = color;
     }

     // Create an action with a name, a color, and an accelerator
     public ColorAction(String name, Color color, char ch, int modifiers) {
       this(name, color);
       putValue(ACCELERATOR_KEY, KeyStroke.getKeyStroke(ch, modifiers));

       // Now find the character to underline
       int index = name.toUpperCase().indexOf(ch);
       if(index != -1) {
         putValue(DISPLAYED_MNEMONIC_INDEX_KEY, index);
       }
     }

     public void actionPerformed(ActionEvent e) {
       elementColor = color;

       // This is temporary just to show it works...
       getContentPane().setBackground(color);
     }

     private Color color;
   }

   // File actions
   private FileAction newAction, openAction, closeAction, saveAction, saveAsAction, printAction, exitAction;
   private FileAction[] fileActions;                                    // File actions as an array

   // Element type actions
   private TypeAction lineAction, rectangleAction, circleAction, curveAction;
   private TypeAction[] typeActions;                                    // Type actions as an array

 // Element color actions
   private ColorAction redAction, yellowAction,greenAction, blueAction;
   private ColorAction[] colorActions;                                  // Color actions as an array

   private JMenuBar menuBar = new JMenuBar();                           // Window menu bar
   private JMenu elementMenu;                                           // Elements menu
   private JMenu colorMenu;                                             // Color menu
   private Color elementColor = DEFAULT_ELEMENT_COLOR;                  // Current element color
   private int elementType = DEFAULT_ELEMENT_TYPE;                      // Current element type
 }

需要3个内部类来定义动作：一个用于File菜单项；第二个用于元素类型菜单项；第三个用于元素颜色菜单项。这些类都派生于实现了Aciton接口的javax.swing.AbstractAction类。AbstractAction类有3个构造函数，无参构造函数会创建带有默认名称和图标的对象；可以仅仅提供String类型的名称参数，此时会获得默认图标；最后，还可以提供名称和Icon类型的图标作为参数。
其它部分和以前一样：

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

 public class Sketcher {
   public static void main(String[] args) {
      theApp = new Sketcher();                                          // Create the application object
    SwingUtilities.invokeLater(new Runnable() {
             public void run() {
                           theApp.createGUI();                          // Call GUI creator
             }
         });
   }

   // Method to create the application GUI
   private void createGUI() {
     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.addWindowListener(new WindowHandler());                     // Add window listener
     window.setVisible(true);
   }

   // Handler class for window events
   class WindowHandler extends WindowAdapter {
     @Override
     // Handler for window closing event
     public void windowClosing(WindowEvent e) {
       // Code to be added here...
     }
   }

   private SketcherFrame window;                                        // The application window
   private static Sketcher theApp;                                      // The application object
 }

导入自定义包文件：

 // Defines application wide constants
 package Constants;
 import java.awt.Color;

 public class SketcherConstants {
   // Element type definitions
   public final static int LINE      = 101;
   public final static int RECTANGLE = 102;
   public final static int CIRCLE    = 103;
   public final static int CURVE     = 104;

   // Initial conditions
   public final static int DEFAULT_ELEMENT_TYPE = LINE;
   public final static Color DEFAULT_ELEMENT_COLOR = Color.BLUE;
 }