Java MessagePanel

一个小测试，MessagePanel继承于Panel,显示结果为：
  1 import java.awt.*;
  2 
  3 import javax.swing.*;
  4 
  5 public class hello extends JFrame{
  6     public hello(){
  7         MessagePanel mp1=new MessagePanel("Welcome to Java");
  8         MessagePanel mp2=new MessagePanel("Java is fun");
  9         MessagePanel mp3=new MessagePanel("Java is cool");
 10         MessagePanel mp4=new MessagePanel("I love Java");
 11         
 12         mp1.setFont(new Font("SansSerif",Font.ITALIC,20));
 13         mp2.setFont(new Font("Courier",Font.BOLD,20));
 14         mp3.setFont(new Font("Times",Font.ITALIC,20));
 15         mp4.setFont(new Font("Californian FB",Font.PLAIN,20));
 16         
 17         mp1.setBackground(Color.red);
 18         mp2.setBackground(Color.cyan);
 19         mp3.setBackground(Color.green);
 20         mp4.setBackground(Color.white);
 21         mp1.setCentered(true);
 22         
 23         setLayout(new GridLayout(2,2));
 24         add(mp1);
 25         add(mp2);
 26         add(mp3);
 27         add(mp4);
 28     }
 29     
 30     public static void main(String[] args){
 31         hello frame=new hello();
 32         frame.setSize(300,200);
 33         frame.setTitle("Test MessagePanel");
 34         frame.setLocationRelativeTo(null);
 35         frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
 36         frame.setVisible(true);
 37     }
 38 }
 39 
 40 
 41 class MessagePanel extends JPanel{
 42     private String message="Welcome to Java";
 43     private int xCoordinate=20;
 44     private int yCoordinate=20;
 45     private boolean centered;
 46     private int interval=10;
 47     public MessagePanel(){}
 48     public MessagePanel(String message){
 49         this.message=message;
 50     }
 51     public String getMessage(){
 52         return message;
 53     }
 54     public void getMessage(String message){
 55         this.message=message;
 56     }
 57     public int getXCoordinate(){
 58         return xCoordinate;
 59     }
 60     public void setXCoordinate(int x){
 61         this.xCoordinate=x;
 62         repaint();
 63     }
 64      public int getYCoordinate(){
 65         return yCoordinate;
 66     }
 67     public void setYCoordinate(int y){
 68         this.yCoordinate=y;
 69         repaint();
 70     }
 71     public boolean isCentered(){
 72         return centered;
 73     }
 74     public void setCentered(boolean centered){
 75         this.centered=centered;
 76         repaint();
 77     }
 78     
 79     public int getInterval(){
 80         return interval;
 81     }
 82     
 83     public void setinterVal(int interval){
 84         this.interval=interval;
 85         repaint();
 86     }
 87     protected void paintComponent(Graphics g){
 88         super.paintComponent(g);
 89         if(centered){
 90             FontMetrics fm = g.getFontMetrics();
 91             int stringWidth=fm.stringWidth(message);
 92             int stringAscent=fm.getAscent();
 93             xCoordinate=getWidth()/2-stringWidth/2;
 94             yCoordinate=getHeight()/2-stringAscent/2;
 95         }
 96         g.drawString(message, xCoordinate, yCoordinate);
 97     }
 98     public void moveLeft(){
 99         xCoordinate-=interval;
100         repaint();
101     }
102     public void moveRight(){
103         xCoordinate+=interval;
104         repaint();
105     }
106 
107     public void moveUp(){
108         yCoordinate-=interval;
109         repaint();
110     }
111     public void moveDown(){
112         yCoordinate+=interval;
113         repaint();
114     }
115     public Dimension getPreferredSize(){
116         return new Dimension(200,30);
117     }
118     
119 }