java - 修复后覆盖未调用的绘制方法

Question

我的问题本质上是创建一个具有几种不同场景的物理引擎。我想通过单独运行每个场景的按钮将不同的场景合并到一个窗口中。框架工作正常，按钮显示并可以按下；然而， pain 方法中的打印行永远不会发生，从那里我得出结论，即使在重新绘制之后，也不会调用绘制。我知道它们不一样，但我不明白为什么在这种情况下与其他情况相比，油漆没有被访问。

  import java.awt.Graphics;
  import java.awt.Graphics2D;
  import java.awt.RenderingHints;
  import java.awt.event.*;
  import javax.swing.JFrame;
  import javax.swing.JPanel;
  import java.awt.Color;
  import javax.swing.JButton;

  public class PhysicsEngine extends JPanel{
     double x ,y;

     JFrame frame;
     JPanel pan;
     JButton b1;
     JButton b2;
     JButton b3;
     JButton b4;
     JButton b5;

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

     public PhysicsEngine(){
        frame = new JFrame("Ball Engine");

        pan = new JPanel();
        frame.add(pan);

        b1 = new JButton("1");
        b1.addActionListener(new ActionListener() {
           public void actionPerformed(ActionEvent event){
              try{
                 startFirst();
              } 
              catch(InterruptedException exception){}
           }
        });
        pan.add(b1);

        b2 = new JButton("2");
        b2.addActionListener(new ActionListener() {
           public void actionPerformed(ActionEvent e){
              try{
                 startSecond();
              } 
              catch(InterruptedException exception){}
           }
        });
        pan.add(b2);


        b3 = new JButton("3");
        b3.addActionListener(new ActionListener() {
           public void actionPerformed(ActionEvent e){
              try{
                 startThird();
              } 
              catch(InterruptedException exception){}
           }
        });
        pan.add(b3);

        b4 = new JButton("4");
        b4.addActionListener(new ActionListener() {
           public void actionPerformed(ActionEvent e){
              try{
                 startFourth();
              } 
              catch(InterruptedException exception){}
           }
        });
        pan.add(b4);

       b5 = new JButton("5");
       b5.addActionListener(new ActionListener() {
          public void actionPerformed(ActionEvent e){
             try{
                startFifth();
             } 
             catch(InterruptedException exception){}
          }
       });
       pan.add(b5);

       frame.setSize(600, 600);
      frame.setVisible(true);
      frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
     }

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

          System.out.println(""+y);

          Graphics2D g2d = (Graphics2D) g;
         g2d.setColor(Color.RED);   
         g2d.fillOval((int)x, (int)y, 30, 30);
    }

     public void startFirst() throws InterruptedException{
        x = 300;

        for(int t = 1;;t++){
           //xPos= 0*t*t + 0*t + 300 this is constant at 300
           if(y>=615) break; //stops the loop when the ball is off the screen

           y = .1*t*t + 0*t + 80; //parametric equation for y
           repaint();
           Thread.sleep(10);
        }
     }

     public void startSecond() throws InterruptedException{
        x = 300;

        for(int t = 1;;t++){
           //xPos= 0*t*t + 0*t + 300 this is constant at 300
           if(y>=615) break; //stops the loop when the ball is off the screen

           y = .1*t*t - 10*t + 550; //parametric equation for y
           repaint();
           Thread.sleep(10);
        }
     }

     public void startThird() throws InterruptedException{      
        for(int t = 1;;t++){
           if(y>=615||x>=615) break; //stops the loop when the ball is off the screen

           y = .1*t*t - 10*t + 550; //parametric equation for y
           x = 0*t*t + 5*t + 50; //parametric equation for x
           repaint();
           Thread.sleep(10);
        }
     }

     public void startFourth() throws InterruptedException{      
        for(int t = 1;;t++){
           //xPos= 0*t*t + 0*t + 300 this is constant at 300
           if(y>=615||x>=615) break; //stops the loop when the ball is off the screen

           y = t*t*t + 50; //given parametric equation for y
           x = t - 4; //given parametric equation for x
           repaint();
           Thread.sleep(10);
        }
     }

     public void startFifth() throws InterruptedException{      
        for(int t = 1;t<500 /* goes for 5 seconds */;t++){        
           y = 200*Math.sin(t) + 300; //given parametric equation for y
           x = 200*Math.cos(t) + 300; //given parametric equation for x
           repaint();
           Thread.sleep(10);
        }
     }
  }

Answer 1

基本问题是您正在重写PhysicsEngine 类的paint() 方法。但您永远不会将此类的实例添加到框架中。

但是，更大的问题是类(class)的结构。您的主类不应该只是为了创建 JFrame 而扩展 JPanel。创建框架的逻辑应位于 main() 方法中，然后您的 PysicsEngine 面板应包含您想要为框架构建的所有组件。另外，自定义绘制应该通过重写 paintComponent(...) 方法而不是 Paint() 方法来完成。

阅读 Swing 教程中关于 Custom Painting 的部分了解基本绘画信息和演示。

然后您可以查看教程中的其他部分，以获得更好的方法来构建代码。例如，如何使用按钮教程中的 ButtonDemo 代码将向您展示如何扩展 JPanel 并向其添加按钮。