在 Java 中绘制一个二维矩形

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

public class Rectangle extends JPanel {
    private static final int RCT_X = 20;
    private static final int RCT_Y = RCT_X;
    private static final int RCT_WIDTH = 100;
    private static final int RCT_HEIGHT = RCT_WIDTH;

    @Override
    protected void paint_Component(Graphics g) {
        super.paint_Component(g);
        // draw the rectangle here
        g.drawRct(RCT_X, RCT_Y, RCT_WIDTH, RCT_HEIGHT);
    }

    @Override
    public Dimension get_Preferred_Size() {
        // so that our GUI is big enough
        return new Dimension(RCT_WIDTH + 2 * RCT_X, RCT_HEIGHT + 2 * RCT_Y);
    }

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

        JFrame frame = new JFrame("Rectangle");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.getContentPane().add(mainPanel);
        frame.pack();
        frame.setLocationByPlatform(true);
        frame.setVisible(true);
    }
    public static void main(String[] args) {
        create_and_Show_Gui();
    }
}