JAVA GUI 代码没有按预期运行

Question

我从书上输入了这段代码

public class SimpleGui3C  {

JFrame frame;


public static void main (String[] args) {
   SimpleGui3C gui = new SimpleGui3C();
   gui.go();
}

public void go() {
   frame = new JFrame("My own code");
   frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

  
   MyDrawPanel drawPanel = new MyDrawPanel();

   frame.getContentPane().add(BorderLayout.CENTER, drawPanel);

   frame.setSize(420,300);
   frame.setVisible(true);
}}

class MyDrawPanel extends JPanel {

public void painComponent(Graphics g) {
    
    g.fillRect(0,0,this.getWidth(), this.getHeight());

    
    int red = (int) (Math.random() * 255);
    int green = (int) (Math.random() * 255);
    int blue = (int) (Math.random() * 255);

    Color randomColor = new Color(red, green, blue);
    g.setColor(randomColor);
    g.fillOval(70,70,100,100);
}}

结果是:

这是本书的原始代码，我从本书的网站上下载了这段代码

public class SimpleGui3C  {

JFrame frame;

public static void main (String[] args) {
   SimpleGui3C gui = new SimpleGui3C();
   gui.go();
}

public void go() {
   frame = new JFrame();
   frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

  
   MyDrawPanel drawPanel = new MyDrawPanel();
   

   frame.getContentPane().add(BorderLayout.CENTER, drawPanel);


   frame.setSize(420,300);
   frame.setVisible(true);
}}

class MyDrawPanel extends JPanel {

  public void paintComponent(Graphics g) {
     
     g.fillRect(0,0,this.getWidth(), this.getHeight());

     // make random colors to fill with
     int red = (int) (Math.random() * 255);
     int green = (int) (Math.random() * 255);
     int blue = (int) (Math.random() * 255);

     Color randomColor = new Color(red, green, blue);
     g.setColor(randomColor);
     g.fillOval(70,70,100,100);
  }}

结果是这样的:

我检查了一遍又一遍，确保它们是一样的，看起来它们是一样的。但为什么 GUI 不同？

请帮助，在此先感谢。

Answer 1

在您自己的代码中，方法名称是 painComponent 而它应该是 paintComponent。

提示:将@Override添加到重写的方法中，然后编译器会告诉你这样的错误:

@Override
public void painComponent(Graphics g) {