即使我将 JPanel 添加到 JFrame，Eclipse 上的 Java 也不会显示 JPanel

Question

这些是文件。我已将 JFrame 设置为可见，并向其中添加了 JPanel，但代码仍然只显示窗口，其中没有任何内容。

import java.util.List;
import java.util.ArrayList;
import java.util.Random;

import javax.swing.JFrame;
import javax.swing.JPanel;
import java.util.Collections;


public static void main(String[] args)
{

    JFrame frame = new JFrame();
    frame.setSize(350, 300);
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.setTitle("My Empty Window");
    frame.setVisible(true);

    DrawingPanel panel = new DrawingPanel();
    
    frame.add(panel);
    frame.setVisible(true);
}

-------------绘图面板文件--------------------

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

 public class DrawingPanel extends JPanel {

      public void painting(Graphics pen) {

         pen.drawRect(50, 50, 20, 20);
         pen.drawRect(100, 50, 40, 20);
         pen.drawOval(200,50,20,20);
         pen.drawOval(250, 50, 40, 20);
         pen.drawString("Square", 50, 90);
         pen.drawString("Rectangle", 100, 90);
         pen.drawString("Cirlce", 200, 90); 
         pen.drawString("Oval", 250, 90);
         pen.fillRect(50, 100, 20, 20);
         pen.fillRect(100, 100, 40, 20);
         pen.fillOval(250, 100, 20, 20);
         pen.fillOval(250, 100, 40, 20);
         pen.drawLine(50, 150, 300, 150);
         pen.drawArc(50, 150, 200, 100, 0, 180);
         pen.fillArc(100, 175, 200, 75, 90, 45);
     }
 }

Answer 1

这是使您的代码可运行、修复您的 JFrame 方法调用并修复您的绘图 JPanel 后得到的结果。

Swing 应用程序应始终以调用 SwingUtilities invokeLater 方法开始。此方法确保在 Event Dispatch Thread 上创建并执行 Swing 组件。 .

您打包一个JFrame。您可以设置绘图 JPanel 的首选尺寸。这样，您就可以知道您的绘图 JPanel 有多大，而不必担心 JFrame 装饰。

这是完整的可运行代码。

import java.awt.Dimension;
import java.awt.Graphics;

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

public class DrawingPanelExample implements Runnable {

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new DrawingPanelExample());
    }

    @Override
    public void run() {
        JFrame frame = new JFrame("My Empty Window");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        DrawingPanel panel = new DrawingPanel();
        frame.add(panel);

        frame.pack();
        frame.setLocationByPlatform(true);
        frame.setVisible(true);
    }

    public class DrawingPanel extends JPanel {

        private static final long serialVersionUID = 1L;

        public DrawingPanel() {
            this.setPreferredSize(new Dimension(350, 300));
        }

        @Override
        protected void paintComponent(Graphics pen) {
            super.paintComponent(pen);

            pen.drawRect(50, 50, 20, 20);
            pen.drawRect(100, 50, 40, 20);
            pen.drawOval(200, 50, 20, 20);
            pen.drawOval(250, 50, 40, 20);
            pen.drawString("Square", 50, 90);
            pen.drawString("Rectangle", 100, 90);
            pen.drawString("Cirlce", 200, 90);
            pen.drawString("Oval", 250, 90);
            pen.fillRect(50, 100, 20, 20);
            pen.fillRect(100, 100, 40, 20);
            pen.fillOval(250, 100, 20, 20);
            pen.fillOval(250, 100, 40, 20);
            pen.drawLine(50, 150, 300, 150);
            pen.drawArc(50, 150, 200, 100, 0, 180);
            pen.fillArc(100, 175, 200, 75, 90, 45);
        }
    }

}