第十章

事件處理

10.1 事件類別

事件來源: 產生事件並管理聽候者(listener)
例: applet
聽候者(listener): 當事件發生時, 被告知
例: MouseListener
事件類別: 描述事件
例: MouseEvent

`MouseListener` 介面

public interface MouseListener
{
   void mousePressed(MouseEvent event);
      //Called when a mouse button has been pressed on a component
   void mouseReleased(MouseEvent event);
      //Called when a mouse button has been released on a component
   void mouseClicked(MouseEvent event);
      //Called when the mouse has been clicked on a component
   void mouseEntered(MouseEvent event);
      //Called when the mouse enters a component 
   void mouseExited(MouseEvent event);
      //Called when the mouse exits a component 
}

File MouseSpy.java

import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;

/**
   This listener simply prints out the listener method name
   and the x- and y-coordinate of the mouse position.
*/
public class MouseSpy implements MouseListener
{
   public void mousePressed(MouseEvent event)
   {
      System.out.println("Mouse pressed. x = "
         + event.getX() + " y = " + event.getY());
   }

   public void mouseReleased(MouseEvent event)
   {
      System.out.println("Mouse released. x = "
         + event.getX() + " y = " + event.getY());
   }

   public void mouseClicked(MouseEvent event)
   {
      System.out.println("Mouse clicked. x = "
         + event.getX() + " y = " + event.getY());
   }

   public void mouseEntered(MouseEvent event)
   {
      System.out.println("Mouse entered. x = "
         + event.getX() + " y = " + event.getY());
   }

   public void mouseExited(MouseEvent event)
   {
      System.out.println("Mouse exited. x = "
         + event.getX() + " y = " + event.getY());
   }
}

File MouseSpyApplet.java

import java.applet.Applet;

/**
   This applet installs a mouse spy. Try generating the
   five mouse event types by moving and clicking the mouse.
*/
public class MouseSpyApplet extends Applet
{
   public MouseSpyApplet()
   {
      MouseSpy listener = new MouseSpy();
      addMouseListener(listener);
   }
}

偵測滑鼠事件

10.2 處理滑鼠輸入

移動長方形的滑鼠聽候者

從事件物件取得滑鼠的位置
存取外一層類別的 box 個體變數
呼用在外一層類別的 repaint 方法
repaint 觸發 paint 方法
總是應呼用 repaint 去觸發 paint 方法
不要直接呼用 paint

public MouseApplet()
{
   ...
   //add mouse press listener 
   class MousePressListener implements MouseListener
   {
      public void mousePressed(MouseEvent event)
      {
         int x = event.getX();
         int y = event.getY();
         box.setLocation(x,y);
         repaint(); 
      }
      //do-nothing methods 
      public void mouseReleased(MouseEvent event){}
      public void mouseClicked(MouseEvent event){}
      public void mouseEntered(MouseEvent event){}
      public void mouseExited(MouseEvent event){}
   }
   MouseListener listener = new MousePressListener();
   addMouseListener(listener);
}

The Mouse Applet

MouseApplet.java

import java.applet.Applet;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Rectangle;
import java.awt.event.MouseListener;
import java.awt.event.MouseEvent;

/**
   This applet lets the user move a rectangle by clicking
   the mouse.
*/
public class MouseApplet extends Applet
{
   public MouseApplet()
   {
      // the rectangle that the paint method draws
      box = new Rectangle(BOX_X, BOX_Y,
         BOX_WIDTH, BOX_HEIGHT);

      // add mouse press listener

      class MousePressListener implements MouseListener
      {
         public void mousePressed(MouseEvent event)
         {
            int x = event.getX();
            int y = event.getY();
            box.setLocation(x, y);
            repaint();
         }

         // do-nothing methods
         public void mouseReleased(MouseEvent event) {}
         public void mouseClicked(MouseEvent event) {}
         public void mouseEntered(MouseEvent event) {}
         public void mouseExited(MouseEvent event) {}
      }

      MouseListener listener = new MousePressListener();
      addMouseListener(listener);
   }

   public void paint(Graphics g)
   {
      Graphics2D g2 = (Graphics2D)g;
      g2.draw(box);
   }

   private Rectangle box;
   private static final int BOX_X = 100;
   private static final int BOX_Y = 100;
   private static final int BOX_WIDTH = 20;
   private static final int BOX_HEIGHT = 30;
}

10.3 處理文字輸入

有控制面板的小程式

控制面板(panel)元件

使用 Swing 套件 javax.swing
類別名稱以 J 起頭
JTextField xField = new JTextField(width);
JLabel xLabel = new JLabel("x = ");
Icon buttonIcon = new ImageIcon("hand.gif");
moveButton = new JButton("Move", buttonIcon);

按鈕聽候者

按下按鈕, 即移動長方形
從含蓋的適用範圍讀取 xField, yField 變數

public ButtonApplet()
{
   ...
   class MoveButtonListener implements ActionListener
   {
      public void actionPerformed(ActionEvent event)
      {
         int x =Integer.parseInt(xField.getText());
         int y =Integer.parseInt(yField.getText());
         box.setLocation(x,y);
         repaint();
      }
   };
   ActionListener listener = new MoveButtonListener();
   moveButton.addActionListener(listener);
   ...
}

在面板中放置元件

JPanel 是元件的容器(container)

在面板中添加元件

JPanel panel = new JPanel();
panel.add(xLabel);
panel.add(xField);
. . .

將面板放入框架(frame)

JFrame frame = new JFrame();
frame.setContentPane(panel);

裝填框架: 調整框架大小, 剛好容得下這些元件
```
frame.pack();
frame.show();
```

File ButtonApplet.java

import java.applet.Applet;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Rectangle;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.ImageIcon;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JTextField;

/**
   This applet lets the user move a rectangle by specifying
   the x- and y-position of the top left corner.
*/
public class ButtonApplet extends Applet
{
   public ButtonApplet()
   {
      // the rectangle that the paint method draws
      box = new Rectangle(BOX_X, BOX_Y,
         BOX_WIDTH, BOX_HEIGHT);

      // the text fields for entering the x- and y-coordinates
      final JTextField xField = new JTextField(5);
      final JTextField yField = new JTextField(5);

      // the button to move the rectangle
      JButton moveButton = new JButton("Move",
          new ImageIcon("hand.gif"));

      class MoveButtonListener implements ActionListener
      {
         public void actionPerformed(ActionEvent event)
         {
            int x = Integer.parseInt(xField.getText());
            int y = Integer.parseInt(yField.getText());
            box.setLocation(x, y);
            repaint();
         }
      }

      ActionListener listener = new MoveButtonListener();
      moveButton.addActionListener(listener);

      // the labels for labeling the text fields
      JLabel xLabel = new JLabel("x = ");
      JLabel yLabel = new JLabel("y = ");

      // the panel for holding the user interface components
      JPanel panel = new JPanel();

      panel.add(xLabel);
      panel.add(xField);
      panel.add(yLabel);
      panel.add(yField);
      panel.add(moveButton);

      // the frame for holding the component panel
      JFrame frame = new JFrame();
      frame.setContentPane(panel);
      frame.pack();
      frame.show();
   }

   public void paint(Graphics g)
   {
      Graphics2D g2 = (Graphics2D)g;
      g2.draw(box);
   }

   private Rectangle box;
   private static final int BOX_X = 100;
   private static final int BOX_Y = 100;
   private static final int BOX_WIDTH = 20;
   private static final int BOX_HEIGHT = 30;
}

10.4 行為類似的按鈕組

有按鈕組的小程式

這四個按鈕要做的工作類似, 界定按鈕的程式碼重覆性很高:

    JButton leftButton = new JButton("Left");

   class LeftButtonListener implements ActionListener
   {
      public void actionPerformed(ActionEvent event)
      {
         box.setLocation(-BOX_WIDTH,0);
         repaint();
      }
   };
   LeftButtonListener leftListener = new ButtonListener();
   leftButton.addActionListener(leftListener);

各個按鈕的程式碼只有在按鈕標記和移動量。

補救: 設計一方法, 可建構四個按鈕中任一個, 而將按鈕標記和移動量當做參數。

public JButton makeButton(String label, final int dx, final int dy)
{
   JButton button = new JButton(label);

   class ButtonListener implements ActionListener
   {
      public void actionPerformed(ActionEvent event)
      {
         box.translate(dx, dy);
         repaint();
      }
   };

   ButtonListener listener = new ButtonListener();
   button.addActionListener(listener);
   return button;
}

注意: 參數 dx 和 dy 宣告為 final。
如此, ButtonListener 才能夠存取這些參數。

呼用 makeButton 方法四次:

panel.add(makeButton("Left",-BOX_WIDTH,0));
panel.add(makeButton("Right",BOX_WIDTH,0));
panel.add(makeButton("Up",0,-BOX_HEIGHT));
panel.add(makeButton("Down",0,BOX_HEIGHT));

File ButtonApplet.java

import java.applet.Applet;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Rectangle;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;

/**
   This applet lets the user move a rectangle by clicking
   on buttons labeled "Left", "Right", "Up", and "Down".
*/
public class ButtonApplet extends Applet
{
   public ButtonApplet()
   {
      // the rectangle that the paint method draws
      box = new Rectangle(BOX_X, BOX_Y,
         BOX_WIDTH, BOX_HEIGHT);

      // the panel for holding the user interface components
      JPanel panel = new JPanel();

      panel.add(makeButton("Left", -BOX_WIDTH, 0));
      panel.add(makeButton("Right", BOX_WIDTH, 0));
      panel.add(makeButton("Up", 0, -BOX_HEIGHT));
      panel.add(makeButton("Down", 0, BOX_HEIGHT));

      // the frame for holding the component panel
      JFrame frame = new JFrame();
      frame.setContentPane(panel);
      frame.pack();
      frame.show();
   }

   public void paint(Graphics g)
   {
      Graphics2D g2 = (Graphics2D)g;
      g2.draw(box);
   }

   /**
      Makes a button that moves the box.
      @param label the label to show on the button
      @param dx the amount by which to move the box in x-direction
      when the button is clicked
      @param dy the amount by which to move the box in y-direction
      when the button is clicked
      @return the button
   */
   public JButton makeButton(String label, final int dx,
      final int dy)
   {
      JButton button = new JButton(label);

      class ButtonListener implements ActionListener
      {
         public void actionPerformed(ActionEvent event)
         {
            box.translate(dx, dy);
            repaint();
         }
      }

      ButtonListener listener = new ButtonListener();
      button.addActionListener(listener);
      return button;
   }

   private Rectangle box;
   private static final int BOX_X = 100;
   private static final int BOX_Y = 100;
   private static final int BOX_WIDTH = 20;
   private static final int BOX_HEIGHT = 30;
}

10.5 框架視窗

應用程式, 不是小程式

建構並顯示框架

JFrame frame = new JFrame();
. . .
frame.show();

設定預設的關閉運算

frame.setDefaultCloseOperation(EXIT_ON_CLOSE);

將元件加入面板, 然後將面板設為內容格(pane)

JPanel panel = new
  JPanel();
panel.add(. . .);
panel.add(. . .)
frame.setContentPane(panel);

A Frame with Two Labels

File FrameTest.java

import javax.swing.ImageIcon;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;

/**
   This program displays a frame with an image and a text label.
*/
public class FrameTest
{
   public static void main(String[] args)
   {
      JFrame frame = new JFrame();
      frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

      JLabel iconLabel = new JLabel(new ImageIcon("world.gif"));
      JLabel textLabel = new JLabel("Hello, World!");

      JPanel panel = new JPanel();
      panel.add(iconLabel);
      panel.add(textLabel);
      frame.setContentPane(panel);

      frame.pack();
      frame.show();
   }
}

10.6 文字元件

JTextField 容納單行文字
JTextArea 容納多行文字
用 new JTextArea(rows, columns) 建構
textArea.append(aString) 在末尾添附文字
textArea.setEditable(false) 只用於顯示

添加卷軸滑桿(scroll bar), 用

JScrollPane scrollPane = new JScrollPane(textArea);
textArea.setContentPane(scrollPane);

A Text Area with Scroll Bars

The Control Panel for Adding Interest

File TextAreaTest.java

import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTextArea;
import javax.swing.JTextField;

/**
   This program shows a frame with a text area that displays
   the growth of an investment. A second frame holds a text
   field to specify the interest rate.
*/
public class TextAreaTest
{
   public static void main(String[] args)
   {
      // the application adds interest to this bank account
      final BankAccount account = new BankAccount(INITIAL_BALANCE);
      // the text area for displaying the results
      final JTextArea textArea = new JTextArea(10, 30);
      textArea.setEditable(false);
      JScrollPane scrollPane = new JScrollPane(textArea);

      // construct the frame for displaying the text area
      JFrame frame = new JFrame();
      frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      frame.setContentPane(scrollPane);
      frame.pack();
      frame.show();

      // the label and text field for entering the interest rate
      JLabel rateLabel = new JLabel("Interest Rate: ");

      final JTextField rateField = new JTextField(10);
      rateField.setText("" + DEFAULT_RATE);

      // the button to trigger the calculation
      JButton calculateButton = new JButton("Add Interest");

      class CalculateListener implements ActionListener
      {
         public void actionPerformed(ActionEvent event)
         {
            double rate = Double.parseDouble(
               rateField.getText());
            double interest = account.getBalance()
               * rate / 100;
            account.deposit(interest);
            textArea.append(account.getBalance() + "\n");
         }
      }

      ActionListener listener = new CalculateListener();
      calculateButton.addActionListener(listener);

      // the control panel that holds the input components
      JPanel controlPanel = new JPanel();
      controlPanel.add(rateLabel);
      controlPanel.add(rateField);
      controlPanel.add(calculateButton);

      // the frame to hold the control panel
      JFrame controlFrame = new JFrame();
      controlFrame.setContentPane(controlPanel);
      controlFrame.pack();
      controlFrame.show();
   }

   private static final double DEFAULT_RATE = 10;
   private static final double INITIAL_BALANCE = 1000;
}

第十章

事件處理

10.1 事件類別

MouseListener 介面

File MouseSpy.java

File MouseSpyApplet.java

偵測滑鼠事件

10.2 處理滑鼠輸入

移動長方形的滑鼠聽候者

The Mouse Applet

MouseApplet.java

10.3 處理文字輸入

有控制面板的小程式

控制面板(panel)元件

按鈕聽候者

在面板中放置元件

File ButtonApplet.java

10.4 行為類似的按鈕組

有按鈕組的小程式

File ButtonApplet.java

10.5 框架視窗

A Frame with Two Labels

File FrameTest.java

10.6 文字元件

A Text Area with Scroll Bars

The Control Panel for Adding Interest

File TextAreaTest.java

`MouseListener` 介面