在JPanel中使用睡眠 [英] Using sleep in JPanel

问题描述

我编写了一个简单的Java程序(在彼此之间经过一些延迟之后)在屏幕上放置了一些矩形

I wrote a simple java program to place some rectangles on the screen (after some delay between each other)

package guitest2;
import java.awt.Graphics;
import javax.swing.JPanel;

public class DrawPanel extends JPanel {
    public void paintComponent( Graphics g) {
        super.paintComponent(g);
        for (int i = 0; i < 10; i++ ) {
           g.drawRect(10+5*i, 10+5*i, 20, 20);
           try{
              Thread.sleep( 2000 );
           }
           catch (InterruptedException ex) { }
        }
    }
}

我在那个班上用过

package guitest2;
import javax.swing.JFrame;
public class Guitest2 {
    public static void main(String[] args) {
        DrawPanel panel = new DrawPanel();
        JFrame app = new JFrame();
        app.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE);
        app.add(panel);
        app.setSize(450, 250);
        app.setVisible(true);
    }    
}

运行上述代码的问题是，未显示正方形. 10 * 2S = 20秒后，显示的最终面板包含所有正方形.我想要的是:

The problem with running the above code is that, the squares are not shown. After 10*2S = 20 seconds, the final panel is shown containing all squares. What I want are:

1-用g.drawRect画一个正方形.

1- Draw a square with g.drawRect.

2-等待2秒

3-删除前一个正方形并绘制一个新正方形.

3- Remove the previous square and draw the new one.

推荐答案

也许您可以使用下面的代码，但我在注释中更改了一些代码.

Maybe you could use the code like below, I changed a bit your code with comments.

    import java.awt.Color;
    import java.awt.Graphics;
    import javax.swing.JPanel;
    import javax.swing.JFrame;

    public class RectTest {
     DrawPanel panel;
     int x;
     int y;
     public static void main(String[] args) {
      new RectTest().startApp();
     } 

     public void startApp() {
      panel = new DrawPanel();
      JFrame app = new JFrame();
      app.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE);
      //modify this line
      app.getContentPane().add(panel);
      app.setSize(450, 250);
      app.setVisible(true);
      //added for loop here
      for (int i = 0; i < 10; i++ ) {
       // x,y here
       x = 10+5*i;
       y = 10+5*i;
       // repaint the panel
       panel.repaint();
       // wait 2sec
       try{
          Thread.sleep( 2000 );
       }
       catch (InterruptedException ex) { }
    }
   }

   class DrawPanel extends JPanel {
    public void paintComponent( Graphics g) {
       //super.paintComponent(g);
       // repaint the backround to see the single reactangles
       g.setColor(Color.white);
       g.fillRect(0, 0, this.getWidth(), this.getHeight());

       g.setColor(Color.green);
       g.drawRect(x, y, 20, 20);
    }
   }
  }

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