java - 简单的 Java 2D 图形 : draw a rectangle?

Question

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Answer 1

要在 Swing 中绘制矩形，您应该:

• 首先，切勿直接在 JFrame 或其他顶级窗口中绘制。
• 而是在 JPanel、JComponent 或其他最终从 JComponent 扩展的类中绘制。
• 您应该覆盖 paintComponent(Graphics g) 方法。
• 一定要调用super方法
• 您应该使用 JVM 提供给方法的 Graphics 对象绘制矩形。
• 你应该阅读 Swing 教程中的绘画。

清楚了吗？

例如，

import java.awt.Dimension;
import java.awt.Graphics;
import javax.swing.*;

public class DrawRect extends JPanel {
   private static final int RECT_X = 20;
   private static final int RECT_Y = RECT_X;
   private static final int RECT_WIDTH = 100;
   private static final int RECT_HEIGHT = RECT_WIDTH;

   @Override
   protected void paintComponent(Graphics g) {
      super.paintComponent(g);
      // draw the rectangle here
      g.drawRect(RECT_X, RECT_Y, RECT_WIDTH, RECT_HEIGHT);
   }

   @Override
   public Dimension getPreferredSize() {
      // so that our GUI is big enough
      return new Dimension(RECT_WIDTH + 2 * RECT_X, RECT_HEIGHT + 2 * RECT_Y);
   }

   // create the GUI explicitly on the Swing event thread
   private static void createAndShowGui() {
      DrawRect mainPanel = new DrawRect();

      JFrame frame = new JFrame("DrawRect");
      frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      frame.getContentPane().add(mainPanel);
      frame.pack();
      frame.setLocationByPlatform(true);
      frame.setVisible(true);
   }

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