Question

java的repaint（）没法重绘，怎么回事？

package chapter17;
import java.awt.*;
import javax.swing.*;
import java.awt.event.*;

public class showRadioButton extends JFrame{

/**
* @param args
*/
showRadioButton(){
creatButtonPanel bp =new creatButtonPanel();
messagePanel mp = new messagePanel();

setLayout(new BorderLayout());
add(bp,BorderLayout.SOUTH);
add(mp,BorderLayout.CENTER);

messagePanel messagepanel = new messagePanel();
setSize(800,600);
setLocationRelativeTo(null);
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
setVisible(true);
}
public static void main(String[] args) {
// TODO 自动生成的方法存根
showRadioButton srb = new showRadioButton();

}
//生成String，并操作String
class messagePanel extends JPanel{
private String s = "Welcome to Java";
private boolean bl = true;
private int x ;
private int y ;

// 第一次绘制图形
protected void paintComponent(Graphics g){
super.paintComponent(g);
// 设置string的位置
if(bl == true){
FontMetrics fm = g.getFontMetrics();
int sw = fm.stringWidth(s)/2;
int sh = fm.getAscent()/2;
x = getWidth()/2 - sw;
y = getHeight()/2 - sh;
//开始绘制sting并且设置布尔值
g.drawString(s,x,y);
bl = false;
}else{
g.drawString(s,x,y);
}
}
//重绘方法
protected void left(){
x = x - 50;
repaint();
}
public void right() {
x = x + 50;
repaint();
}
}

//绘制button按钮并出册事件

class creatButtonPanel extends JPanel{
public creatButtonPanel(){
JButton jbtl = new JButton("left");
JButton jbtr = new JButton("rigtht");
jbtl.setMnemonic('L');
jbtr.setMnemonic('R');
//showRadioButton srb = new showRadioButton();

add(jbtl);
add(jbtr);
jbtl.addActionListener(new ActionListener(){
public void actionPerformed(ActionEvent e){
new messagePanel().left(); // 重要 外部类调用内部类
}
});
jbtl.addActionListener(new ActionListener(){
public void actionPerformed(ActionEvent e){
new messagePanel().right();
}
});
//return buttonPanel;
}
}

}
在线等呀

Answer 1

package chapter17;

import java.awt.*;
import javax.swing.*;
import java.awt.event.*;

public class showRadioButton extends JFrame{
	/**
	* @param args
	*/
	messagePanel mp;
	showRadioButton(){
		creatButtonPanel bp =new creatButtonPanel();
		mp = new messagePanel();
		
		setLayout(new BorderLayout());
		add(bp,BorderLayout.SOUTH);
		add(mp,BorderLayout.CENTER);
		
		messagePanel messagepanel = new messagePanel();
		setSize(800,600);
		setLocationRelativeTo(null);
		setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		setVisible(true);
	}
	public static void main(String[] args) {
		// TODO 自动生成的方法存根
		showRadioButton srb = new showRadioButton();
	}
	//生成String，并操作String
	class messagePanel extends JPanel{
		private String s = "Welcome to Java";
		private boolean bl = true;
		private int x ;
		private int y ;
		
		// 第一次绘制图形
		protected void paintComponent(Graphics g){
			super.paintComponent(g);
			// 设置string的位置   
			if(bl == true){
				FontMetrics fm = g.getFontMetrics();
				int sw = fm.stringWidth(s)/2;
				int sh = fm.getAscent()/2;
				x = getWidth()/2 - sw;
				y = getHeight()/2 - sh;
				//开始绘制sting并且设置布尔值
			   g.drawString(s,x,y);
			   bl = false;
			}else{
				g.drawString(s,x,y);
			}
		}
		//重绘方法
		protected  void left(){
			x = x - 50;
			repaint();
		}
		public void right() {
			x = x + 50;
			repaint();
		}
	}
	
	//绘制button按钮并出册事件
	
	class creatButtonPanel extends JPanel{
		public creatButtonPanel(){
		JButton jbtl = new JButton("left");
		JButton jbtr = new JButton("rigtht");
		jbtl.setMnemonic('L');
		jbtr.setMnemonic('R');
		//showRadioButton srb = new showRadioButton();

		add(jbtl);
		add(jbtr);
		jbtl.addActionListener(new ActionListener(){
			public void actionPerformed(ActionEvent e){
				mp.left();                   // 重要   外部类调用内部类
			}
		});
		jbtr.addActionListener(new ActionListener(){
			public void actionPerformed(ActionEvent e){
				mp.right();
			}
		});
		//return buttonPanel;
		}
	}
}