16.6
习题标准答案:
![](https://images.cnblogs.com/OutliningIndicators/ContractedBlock.gif)
1 import java.awt.*; 2 import java.awt.event.*; 3 import javax.swing.*; 4 5 public class Exercise16_6 extends JFrame { 6 private DisplayPanel panel = new DisplayPanel(); 7 8 public Exercise16_6() { 9 add(panel, BorderLayout.CENTER); 10 panel.setFocusable(true); 11 } 12 13 /** Main method */ 14 public static void main(String[] args) { 15 JFrame frame = new Exercise16_6(); 16 frame.setTitle("Exercise16_6"); 17 frame.setSize(300, 300); 18 frame.setLocationRelativeTo(null); // Center the frame 19 frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 20 frame.setVisible(true); 21 } 22 23 class DisplayPanel extends MessagePanel { 24 private String m1 = "Java is fun"; 25 private String m2 = "Java is powerful"; 26 private boolean isM1; 27 28 public DisplayPanel() { 29 setCentered(true); 30 this.addMouseListener(new MouseAdapter() { 31 public void mouseClicked(MouseEvent e) { 32 if (isM1) setMessage(m1); 33 else setMessage(m2); 34 35 isM1 = !isM1; 36 } 37 }); 38 } 39 } 40 }
我的答案:
![](https://images.cnblogs.com/OutliningIndicators/ContractedBlock.gif)
1 import java.awt.*; 2 import java.awt.event.*; 3 import javax.swing.*; 4 5 public class Test_16_6 extends JFrame { 6 MessagePanel mPanel = new MessagePanel(); 7 8 public Test_16_6() { 9 add(mPanel); 10 mPanel.addMouseListener(new mouseListener()); 11 } 12 13 /** Main method */ 14 public static void main(String[] args) { 15 JFrame frame = new Test_16_6(); 16 frame.setTitle("Exercise16_6"); 17 frame.setSize(300, 300); 18 frame.setLocationRelativeTo(null); // Center the frame 19 frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 20 frame.setVisible(true); 21 } 22 23 class mouseListener implements MouseListener{ 24 boolean clicked = false; 25 @Override 26 public void mouseClicked(MouseEvent e) { 27 // TODO Auto-generated method stub 28 if(clicked == false) 29 { mPanel.setMessage("Java is fun"); clicked = true; } 30 else if(clicked == true) 31 { mPanel.setMessage("Java is powerful"); clicked = false;} 32 } 33 @Override 34 public void mouseEntered(MouseEvent e) { 35 // TODO Auto-generated method stub 36 37 } 38 @Override 39 public void mouseExited(MouseEvent e) { 40 // TODO Auto-generated method stub 41 42 } 43 @Override 44 public void mousePressed(MouseEvent e) { 45 // TODO Auto-generated method stub 46 47 } 48 @Override 49 public void mouseReleased(MouseEvent e) { 50 // TODO Auto-generated method stub 51 52 } 53 } 54 }
需要用到的类:
![](https://images.cnblogs.com/OutliningIndicators/ContractedBlock.gif)
1 // MessagePanel.java: Display a message on a JPanel 2 import java.awt.Font; 3 import java.awt.FontMetrics; 4 import java.awt.Dimension; 5 import java.awt.Graphics; 6 import javax.swing.JPanel; 7 8 public class MessagePanel extends JPanel { 9 /** The message to be displayed */ 10 private String message = "Welcome to Java"; 11 12 /** The x coordinate where the message is displayed */ 13 private int xCoordinate = 20; 14 15 /** The y coordinate where the message is displayed */ 16 private int yCoordinate = 20; 17 18 /** Indicate whether the message is displayed in the center */ 19 private boolean centered; 20 21 /** The interval for moving the message horizontally and vertically */ 22 private int interval = 10; 23 24 /** Default constructor */ 25 public MessagePanel() { 26 } 27 28 /** Constructor with a message parameter */ 29 public MessagePanel(String message) { 30 this.message = message; 31 } 32 33 /** Return message */ 34 public String getMessage() { 35 return message; 36 } 37 38 /** Set a new message */ 39 public void setMessage(String message) { 40 this.message = message; 41 repaint(); 42 } 43 44 /** Return xCoordinator */ 45 public int getXCoordinate() { 46 return xCoordinate; 47 } 48 49 /** Set a new xCoordinator */ 50 public void setXCoordinate(int x) { 51 this.xCoordinate = x; 52 repaint(); 53 } 54 55 /** Return yCoordinator */ 56 public int getYCoordinate() { 57 return yCoordinate; 58 } 59 60 /** Set a new yCoordinator */ 61 public void setYCoordinate(int y) { 62 this.yCoordinate = y; 63 repaint(); 64 } 65 66 /** Return centered */ 67 public boolean isCentered() { 68 return centered; 69 } 70 71 /** Set a new centered */ 72 public void setCentered(boolean centered) { 73 this.centered = centered; 74 repaint(); 75 } 76 77 /** Return interval */ 78 public int getInterval() { 79 return interval; 80 } 81 82 /** Set a new interval */ 83 public void setInterval(int interval) { 84 this.interval = interval; 85 repaint(); 86 } 87 88 /** Paint the message */ 89 protected void paintComponent(Graphics g) { 90 super.paintComponent(g); 91 92 if (centered) { 93 // Get font metrics for the current font 94 FontMetrics fm = g.getFontMetrics(); 95 96 // Find the center location to display 97 int stringWidth = fm.stringWidth(message); 98 int stringAscent = fm.getAscent(); 99 // Get the position of the leftmost character in the baseline 100 xCoordinate = getWidth() / 2 - stringWidth / 2; 101 yCoordinate = getHeight() / 2 + stringAscent / 2; 102 } 103 104 g.drawString(message, xCoordinate, yCoordinate); 105 } 106 107 /** Move the message left */ 108 public void moveLeft() { 109 xCoordinate -= interval; 110 repaint(); 111 } 112 113 /** Move the message right */ 114 public void moveRight() { 115 xCoordinate += interval; 116 repaint(); 117 } 118 119 /** Move the message up */ 120 public void moveUp() { 121 yCoordinate -= interval; 122 repaint(); 123 } 124 125 /** Move the message down */ 126 public void moveDown() { 127 yCoordinate -= interval; 128 repaint(); 129 } 130 131 /** Override get method for preferredSize */ 132 public Dimension getPreferredSize() { 133 return new Dimension(200, 30); 134 } 135 }
效果图: