Java之事件处理

监听器

ActionListener接口 ——通常用自己创建的新类implements接口

建议使用匿名内部类实现，因为内部类可以访问类内的变量，而匿名类可以大大简化代码，不需要构造函数。

实例：处理按钮点击事件

 1 package button;
 2 
 3 import java.awt.*;
 4 import java.awt.event.*;
 5 import javax.swing.*;
 6 
 7 /**
 8  * A frame with a button panel
 9  */
10 public class ButtonFrame extends JFrame
11 {
12    private JPanel buttonPanel;
13    private static final int DEFAULT_WIDTH = 300;
14    private static final int DEFAULT_HEIGHT = 200;
15 
16    public ButtonFrame()
17    {      
18       setSize(DEFAULT_WIDTH, DEFAULT_HEIGHT);
19 
20       // create buttons
21       JButton yellowButton = new JButton("Yellow");
22       JButton blueButton = new JButton("Blue");
23       JButton redButton = new JButton("Red");
24 
25       buttonPanel = new JPanel();
26 
27       // add buttons to panel
28       buttonPanel.add(yellowButton);
29       buttonPanel.add(blueButton);
30       buttonPanel.add(redButton);
31 
32       // add panel to frame
33       add(buttonPanel);
34 
35       // create button actions
36       ColorAction yellowAction = new ColorAction(Color.YELLOW);
37       ColorAction blueAction = new ColorAction(Color.BLUE);
38       ColorAction redAction = new ColorAction(Color.RED);
39 
40       // associate actions with buttons
41       yellowButton.addActionListener(yellowAction);
42       blueButton.addActionListener(blueAction);
43       redButton.addActionListener(redAction);
44    }
45 
46    /**
47     * An action listener that sets the panel's background color.
48     */
49    private class ColorAction implements ActionListener
50    {
51       private Color backgroundColor;
52 
53       public ColorAction(Color c)
54       {
55          backgroundColor = c;
56       }
57 
58       public void actionPerformed(ActionEvent event)
59       {
60          buttonPanel.setBackground(backgroundColor);
61       }
62    }
63 }

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实例：改变观感

 1 package plaf;
 2 
 3 import java.awt.event.*;
 4 import javax.swing.*;
 5 
 6 /**
 7  * A frame with a button panel for changing look and feel
 8  */
 9 public class PlafFrame extends JFrame
10 {
11    private JPanel buttonPanel;
12    public PlafFrame()
13    {
14       buttonPanel = new JPanel();
15       
16       UIManager.LookAndFeelInfo[] infos = UIManager.getInstalledLookAndFeels();
17       for (UIManager.LookAndFeelInfo info : infos)
18          makeButton(info.getName(), info.getClassName());
19       
20       add(buttonPanel);
21       pack();
22    }
23 
24    /**
25     * Makes a button to change the pluggable look and feel.
26     * @param name the button name
27     * @param plafName the name of the look and feel class
28     */
29    void makeButton(String name, final String plafName)
30    {
31       // add button to panel
32 
33       JButton button = new JButton(name);
34       buttonPanel.add(button);
35 
36       // set button action
37 
38       button.addActionListener(new ActionListener()
39          {
40             public void actionPerformed(ActionEvent event)
41             {
42                // button action: switch to the new look and feel
43                try
44                {
45                   UIManager.setLookAndFeel(plafName);
46                   SwingUtilities.updateComponentTreeUI(PlafFrame.this);
47                   pack();
48                }
49                catch (Exception e)
50                {
51                   e.printStackTrace();
52                }
53             }
54          });
55    }  
56 }

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适配器

由WindowAdapter类实现的WindowListener接口中的众多方法

由于ActionListener接口只有一个方法所以不需要提供适配器类

动作

Action接口由AbstractAction类实现包含以下方法：

void actionPerformed(ActionEvent event); //扩展于ActionListener接口
void setEnabled(boolean b); //启用或禁用这个这个动作
boolean isEnabled(); //检查动作是否启用
void putValue(String key, Object value); //存储名/值对到动作对象中
Object getvalue(String key); //检索动作对象中的任意名/值对
void addPropertyChangeListener(PropertyChangeListener listener);
void remove PropertyChangeListener(PropertyChangeListener listener); 
//最后两个方法能够让其他对象在动作对象的属性发生变化时得到通告

预定义的动作表名称
名称	值
NAME	动作名称，显示在按钮和菜单上
SMALL_ICON	存储小图标的地方；显示在按钮、菜单项或工具栏中
SHORT_DESCRIPTION	图标的简要说明；显示在工具提示中
LONG_DESCRIPTION	图标的详细说明；显示在在线帮助中。没有Swing组件使用这个值
MNEMONIC_KEY	快捷键缩写；显示在菜单项中
ACCELERATOR_KEY	存储加速击键的地方；Swing组件不使用这个值
ACTION_COMMAND_KEY	历史遗留；仅在旧版本的registerKeyboardAction方法中使用
DEFAULT	常用的综合属性；Swing组件不使用这个值

键盘事件

KeyStroke类将击键与动作相关联

每个组件可以有三个输入映射InputMap和一个动作映射ActionMap 用get获取 put改变

输入映射条件
标志	激活动作
WHEN_FOCUSED	当这个组件拥有键盘焦点时
WHEN_ANCESTOR_OF_FOCUSED_COMPONENT	当这个组件包含了拥有键盘焦点的组件时
WHEN_IN_FOCUSED_WINDOW	当这个组件被包含在一个拥有键盘焦点组件的窗口中时

动作实例：

 1 package action;
 2 
 3 import java.awt.*;
 4 import java.awt.event.*;
 5 import javax.swing.*;
 6 
 7 /**
 8  * A frame with a panel that demonstrates color change actions.
 9  */
10 public class ActionFrame extends JFrame
11 {
12    private JPanel buttonPanel;
13    private static final int DEFAULT_WIDTH = 300;
14    private static final int DEFAULT_HEIGHT = 200;
15 
16    public ActionFrame()
17    {
18       setSize(DEFAULT_WIDTH, DEFAULT_HEIGHT);
19 
20       buttonPanel = new JPanel();
21 
22       // define actions
23       Action yellowAction = new ColorAction("Yellow", new ImageIcon("yellow-ball.gif"),
24             Color.YELLOW);
25       Action blueAction = new ColorAction("Blue", new ImageIcon("blue-ball.gif"), Color.BLUE);
26       Action redAction = new ColorAction("Red", new ImageIcon("red-ball.gif"), Color.RED);
27 
28       // add buttons for these actions
29       buttonPanel.add(new JButton(yellowAction));
30       buttonPanel.add(new JButton(blueAction));
31       buttonPanel.add(new JButton(redAction));
32 
33       // add panel to frame
34       add(buttonPanel);
35 
36       // associate the Y, B, and R keys with names
37       InputMap imap = buttonPanel.getInputMap(JComponent.WHEN_ANCESTOR_OF_FOCUSED_COMPONENT);
38       imap.put(KeyStroke.getKeyStroke("ctrl Y"), "panel.yellow");
39       imap.put(KeyStroke.getKeyStroke("ctrl B"), "panel.blue");
40       imap.put(KeyStroke.getKeyStroke("ctrl R"), "panel.red");
41 
42       // associate the names with actions
43       ActionMap amap = buttonPanel.getActionMap();
44       amap.put("panel.yellow", yellowAction);
45       amap.put("panel.blue", blueAction);
46       amap.put("panel.red", redAction);
47    }
48    
49    public class ColorAction extends AbstractAction
50    {
51       /**
52        * Constructs a color action.
53        * @param name the name to show on the button
54        * @param icon the icon to display on the button
55        * @param c the background color
56        */
57       public ColorAction(String name, Icon icon, Color c)
58       {
59          putValue(Action.NAME, name);
60          putValue(Action.SMALL_ICON, icon);
61          putValue(Action.SHORT_DESCRIPTION, "Set panel color to " + name.toLowerCase());
62          putValue("color", c);
63       }
64 
65       public void actionPerformed(ActionEvent event)
66       {
67          Color c = (Color) getValue("color");
68          buttonPanel.setBackground(c);
69       }
70    }
71 }

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鼠标事件

如果只希望用户点击按钮或菜单，则不需要显式地处理鼠标事件。然而，如果希望用户使用鼠标画图，就需要捕获鼠标移动点击和拖动事件。

鼠标点击事件：

MouseHandler类 extends MouseAdapter类 implement MouseListener接口

鼠标第一次被按下时，调用mouse Pressed方法；鼠标被释放时调用mouseReleased方法；最后调用mouseClicked方法。如果只对最终的点击事件感兴趣，可以忽略前两个方法。

扩展——getModifiersEx方法能够准确地报告鼠标事件的鼠标按钮和键盘修饰符。有下列掩码

　　BUTTON1_DOWN_MASK

　　BUTTON2_DOWN_MASK

　　BUTTON3_DOWN_MASK

　　SHIFT_DOWN_MASK

　　CTRL_DOWN_MASK

　　ALT_DOWN_MASK

　　ALT_GRAPH_DOWN_MASK

　　META_DOWN_MASK

鼠标移动与拖动事件：

MouseMotionHandler类 implement MouseMotionListener接口

鼠标移动调用mouseMoved方法，鼠标拖动调用mouseDragged方法。

鼠标光标可以参考Cursor类的getPredefinedCursor方法。

  1 package mouse;
  2 
  3 import java.awt.*;
  4 import java.awt.event.*;
  5 import java.awt.geom.*;
  6 import java.util.*;
  7 import javax.swing.*;
  8 
  9 /**
 10  * A component with mouse operations for adding and removing squares.
 11  */
 12 public class MouseComponent extends JComponent
 13 {
 14    private static final int DEFAULT_WIDTH = 300;
 15    private static final int DEFAULT_HEIGHT = 200;
 16 
 17    private static final int SIDELENGTH = 10;
 18    private ArrayList<Rectangle2D> squares;
 19    private Rectangle2D current; // the square containing the mouse cursor
 20 
 21    public MouseComponent()
 22    {
 23       squares = new ArrayList<>();
 24       current = null;
 25 
 26       addMouseListener(new MouseHandler());
 27       addMouseMotionListener(new MouseMotionHandler());
 28    }
 29 
 30    public void paintComponent(Graphics g)
 31    {
 32       Graphics2D g2 = (Graphics2D) g;
 33 
 34       // draw all squares
 35       for (Rectangle2D r : squares)
 36          g2.draw(r);
 37    }
 38 
 39    /**
 40     * Finds the first square containing a point.
 41     * @param p a point
 42     * @return the first square that contains p
 43     */
 44    public Rectangle2D find(Point2D p)
 45    {
 46       for (Rectangle2D r : squares)
 47       {
 48          if (r.contains(p)) return r;
 49       }
 50       return null;
 51    }
 52 
 53    /**
 54     * Adds a square to the collection.
 55     * @param p the center of the square
 56     */
 57    public void add(Point2D p)
 58    {
 59       double x = p.getX();
 60       double y = p.getY();
 61 
 62       current = new Rectangle2D.Double(x - SIDELENGTH / 2, y - SIDELENGTH / 2, SIDELENGTH,
 63             SIDELENGTH);
 64       squares.add(current);
 65       repaint();
 66    }
 67 
 68    /**
 69     * Removes a square from the collection.
 70     * @param s the square to remove
 71     */
 72    public void remove(Rectangle2D s)
 73    {
 74       if (s == null) return;
 75       if (s == current) current = null;
 76       squares.remove(s);
 77       repaint();
 78    }
 79 
 80    private class MouseHandler extends MouseAdapter
 81    {
 82       public void mousePressed(MouseEvent event)
 83       {
 84          // add a new square if the cursor isn't inside a square
 85          current = find(event.getPoint());
 86          if (current == null) add(event.getPoint());
 87       }
 88 
 89       public void mouseClicked(MouseEvent event)
 90       {
 91          // remove the current square if double clicked
 92          current = find(event.getPoint());
 93          if (current != null && event.getClickCount() >= 2) remove(current);
 94       }
 95    }
 96 
 97    private class MouseMotionHandler implements MouseMotionListener
 98    {
 99       public void mouseMoved(MouseEvent event)
100       {
101          // set the mouse cursor to cross hairs if it is inside
102          // a rectangle
103 
104          if (find(event.getPoint()) == null) setCursor(Cursor.getDefaultCursor());
105          else setCursor(Cursor.getPredefinedCursor(Cursor.CROSSHAIR_CURSOR));
106       }
107 
108       public void mouseDragged(MouseEvent event)
109       {
110          if (current != null)
111          {
112             int x = event.getX();
113             int y = event.getY();
114 
115             // drag the current rectangle to center it at (x, y)
116             current.setFrame(x - SIDELENGTH / 2, y - SIDELENGTH / 2, SIDELENGTH, SIDELENGTH);
117             repaint();
118          }
119       }
120    }
121    
122    public Dimension getPreferredSize() { return new Dimension(DEFAULT_WIDTH, DEFAULT_HEIGHT); }
123 }

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AWT事件继承层次

AWT事件类的继承关系

事件处理总结
事件		接口	方法	访问方法	事件源
语义事件类	ActionEvent	ActionListener	actionPerformed	getActionCommand getModifiers	AbstractButton JComboBox JTextField Timer
	AdjustmentEvent	AdjustmentListener	adjustmentValueChanged	getAdjustable getAdjustmentType getValue	JScrollbar
	ItemEvent	ItemListener	itemStateChanged	getIten getItemSelectable getStateChange	AbstractButton JComboBox
低级事件类	FocusEvent	FocusListener	focusGained focusLost	isTemporary	Component
	KeyEvent	KeyListener	keyPressed keyReleased keyTyped	getKeyChar getKeyCode getKeyModifiersText getKeyText isActionKey	Component
	MouseEvent	MouseListener	mousePressed mouseReleased mouseEntered mouseExited mouseClicked	getClickCount getX getY getPoint translatePoint	Component
	MouseEvent	MouseMotionListener	mouseDragged mouseMoved		Component
	MouseWheelEvent	MouseWheelListener	mouseWheelMoved	getWheelRotation getScrollAmount	Component
	WindowEvent	WindowListener	windowClosing windowOpened windowIconified windowDeiconified windowClosed windowActivated windowDeactivated	getWindow	Window
	WindowEvent	WindowFocusListener	windowGainFocus windowLostFocus	getOppositeWindow	Window
	WindowEvent	WindowStateListener	windowStateChanged	getOldState getNewState	Window