Question

Graphics在Jpanel上画图 出现空指针 怎么回事 求大神啊 ！代码如下 在测试类中先设置了setVisible(true)

package cn.yzg;

import java.awt.Graphics;
import java.util.Stack;

import javax.swing.JFrame;
import javax.swing.JPanel;

public class Circle {
int x,y;
Stack <Circle> c;
public Circle(int x,int y){
this.x=x;
this.y=y;
}

public void paint(Circle circle,JPanel panel){
Graphics g = panel.getGraphics(); //此处出错
g.drawOval(x, y, 20, 20);
g.fillOval(x, y, 20, 20);
c.push(circle);
}

public void delete(){
if(!c.isEmpty()){
c.pop();
}
}

}
//这是我的测试类
public class Test extends JFrame{
Mingling m =new PaintCircle();
Request request =new Request();
public Test(){
super();
this.setLayout(new BorderLayout());
this.setSize(200, 300);
this.setVisible(true);
this.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
this.add(request.getLabel1(),BorderLayout.NORTH);
this.add(request.getPanel(),BorderLayout.CENTER);
this.add(request.getLabel2(),BorderLayout.SOUTH);

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

}
}

Answer 1

大哥，你给的不全啊

Answer 2

public class Circle extends JPanel {
……

public void paint(Graphics g){
……