Java:用drawLine绘制矩形螺旋线

Question

我正在做一个Java编程练习，我应该用drawLine方法绘制一个矩形螺旋。这是我到目前为止所得到的，但螺旋看起来不完整。

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

public class RectSpiral extends JPanel
{
    public void paintComponent(Graphics g)
    {
        int width = getSize().width;
        int height = getSize().height;

        int widthCenter = width / 2;
        int heightCenter = height / 2;

        for (int i = 0; i < 4 ; i++)
        {
            g.drawLine(widthCenter + (20 * i), heightCenter + (20 * i), widthCenter + (20 * i), heightCenter + 20 + (20 * i));
            g.drawLine(widthCenter + (20 * i), heightCenter + 20 + (20 * i), widthCenter - 20 - (20 * i), heightCenter + 20 + (20 * i));
            g.drawLine(widthCenter - 20 - (20 * i), heightCenter + 20 + (20 * i), widthCenter - 20 - (20 * i), heightCenter - 20 - (20 * i));
            g.drawLine(widthCenter - 20 - (20 * i), heightCenter - 20 - (20 * i), widthCenter + 20 + (20 * i), heightCenter - 20 - (20 * i));
        }
    }

    public static void main(String[] args)
    {
        RectSpiral panel = new RectSpiral();

        JFrame application = new JFrame();

        application.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        application.add(panel);      
        application.setSize(300, 300); 
        application.setVisible(true);     
    }
}

这是输出:

我尝试在 for 循环中添加第五行，但结果仍然不完整。感谢任何帮助，谢谢!

Answer 1

在你的第一个g.drawLine中，你需要从y的中心减去(20 * i)，才能不开始

|
|
|
center
|
|<-center + (20 * i)
|

但是这里:

|
|<-center - (20 * i)
|
center
|
|
|

所以使用

g.drawLine(widthCenter + (20 * i), heightCenter - (20 * i),
//                                              ^---------------change
           widthCenter + (20 * i), heightCenter + 20 + (20 * i));