Question

java中color类怎么调用，和设置数值啊，好多次都出现错误，求解答，一下面的这个程序为例

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

public class MouseDemo3 extends JFrame implements MouseListener,MouseMotionListener{

int flag;
int x=0;
int y=0;
int startx,starty,endx,endy;

public MouseDemo3(){
Container contentPane=getContentPane();
contentPane.addMouseListener(this);
contentPane.addMouseMotionListener(this);
setSize(300,300);
show();
addWindowListener(new WindowAdapter(){
public void windowClosing(WindowEvent e){
System.exit(0);
}
});
}

public void mousePressed(MouseEvent e){
startx=e.getX();
starty=e.getY();
}

public void mouseReleased(MouseEvent e){
endx=e.getX();
endy=e.getY();
}

public void mouseEntered(MouseEvent e){
}

public void mouseExited(MouseEvent e){
}

public void mouseClicked(MouseEvent e){
}

public void mouseMoved(MouseEvent e){
flag=1;
x=e.getX();
y=e.getY();
repaint();
}

public void mouseDragged(MouseEvent e){
flag=2;
x=e.getX();
y=e.getY();
repaint();
}

public void update(Graphics g){
g.setColor(this.getBackground());
g.fillRect(0,0,getWidth(),getHeight());
paint(g);
}

public void paint(Graphics g){
g.setColor(Color.red);//主要是这！！
if(flag==1){
g.drawString("鼠标坐标：("+x+" ,"+y+" )",10,50);
g.drawLine(startx,starty,endx,endy);
}
if(flag==2){
g.drawString("拖曳鼠标坐标：("+x+","+y+")",10,50);
g.drawLine(startx,starty,x,y);
}
}

public static void main(String[] args){
new MouseDemo3();
}
}

Answer 1

public void paint(Graphics g){
super.paint(g);
……
}

在这里加上一句super.paint(g);

这个方法本身它要画出面板，你覆盖后不super一下，面板都出不来