Question

repaint()如何不覆盖原来图形

import java.awt.Canvas;
import java.awt.Color;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;

import javax.swing.JDesktopPane;
import javax.swing.JFrame;
import javax.swing.JInternalFrame;
import javax.swing.JPanel;

public class Test extends JFrame implements MouseListener {
int x;
int y;
int flag;

public static void main(String[] args){
Test test= new Test();
test.setVisible(true);
}

public Test() {
setSize(300,200);
DrawPanel drawtable= new DrawPanel();
drawtable.addMouseListener(this);
setContentPane(drawtable);

}
public class DrawPanel extends JPanel{
public void paint(Graphics g){
Graphics2D g2= (Graphics2D) g;
if(flag==1){
draw1(g2,x,y);
System.out.println(x);
System.out.println(y);

}

}
public void draw1(Graphics2D g2,int x,int y){
g2.setColor(Color.BLACK);
g2.fillRect(x, y, 10,10);

}

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

}

@Override
public void mousePressed(MouseEvent e) {
// TODO Auto-generated method stub

}

@Override
public void mouseReleased(MouseEvent e) {
// TODO Auto-generated method stub

}

@Override
public void mouseEntered(MouseEvent e) {
// TODO Auto-generated method stub

}

@Override
public void mouseExited(MouseEvent e) {
// TODO Auto-generated method stub

}
}
代码如下，我想每次在鼠标点击的地方绘制一个方块，可以多次绘制，然而每次绘制新的方块时，原有方块就消失了，怎么解决呢

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Answer 1

如下代码:
public void paint(Graphics g){ Graphics2D g2=(Graphics2D)g; //加上以下两句,将背景重绘 g2.setColor(getContentPane().getBackground()); g2.fillRect(0,0,getContentPane().getWidth(),getContentPane().getHeight()); g2.setColor(Color.blue); g2.fillRect(fg.getx(), fg.gety(), h, w); }

Answer 2

把原来的保存下来、paint的时候，先绘原来的