Question

求大神看看我的java程序哪里错了

import javax.swing.*;
import java.awt.*;
public class SimpleAnimation{

int x=70;
int y=70;
public static void main (String[] args){
SimpleAnimation gui=new SimpleAnimation ();
gui.go();
}
public void go () {
JFrame frame = new JFrame();
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
MyDrawPanel drawPanel = new MyDrawPanel();
frame.getContentPane().add(drawPanel);
frame.setSize(300,300);
frame.setVisible(true);
for (int i=0;i<130;i++){
x++;
y++;
drawPanel.repaint();
try{
Thread.sleep(50);
} catch(Exception ex) { }
}
}
class MyDrawPanel extends Jpanel{
public void paintComponent(Graphics g) {
g.setColor(Color.green);
g.fillOval(x,y,40,40);
}
}
}

Answer 1

package com.zju.lld;

import javax.swing.*;

import java.awt.*;
public class SimpleAnimation{

int x=70;
int y=70;
public static void main (String[] args){
SimpleAnimation gui=new SimpleAnimation ();
gui.go();
}
public void go () {
JFrame frame = new JFrame();
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
MyDrawPanel drawPanel = new MyDrawPanel();
frame.getContentPane().add(drawPanel);
frame.setSize(300,300);
frame.setVisible(true);
for (int i=0;i<130;i++){
x++;
y++;
drawPanel.repaint();
try{
Thread.sleep(50);
} catch(Exception ex) { }
}
}
class MyDrawPanel extends JPanel{
public void paintComponent(Graphics g) {
g.setColor(Color.green);
g.fillOval(x,y,40,40);
}
}
}

拿去运行吧

追问

谢谢

Answer 2

class MyDrawPanel extends Jpanel 中Jpanel类名写错了。应该改为JPanel，P要大写。

追问

谢谢

Answer 3

JPanel

 class MyDrawPanel extends Jpanel 中没有Jpanel这个类。 要继承 JPanel
 
 其他没有问题。
 
 请采纳。

Answer 4

报的什么错啊
frame.getContentPane().add(drawPanel);报空指针的吗

追问

就这个错误