Exercise : Spiral

Write a Java program that draws the following output using a for loop.

• window size: 170 x 170 px
• "spiral" lines starting from (0, 10), going right 160, down 150, left 150, up 140, right 140, down 130, left 130, up 120, ...

Exercise - answer

import java.awt.*;

public class Spiral {
    public static void main(String[] args) {
        DrawingPanel panel = new DrawingPanel(170, 170);
        Graphics g = panel.getGraphics();
        for (int i = 0; i < 8; i++) {
            g.drawLine(      10*i,   10 + 10*i, 160 - 10*i,  10 + 10*i);  // top
            g.drawLine(160 - 10*i,   10 + 10*i, 160 - 10*i, 160 - 10*i);  // right
            g.drawLine( 10 + 10*i,  160 - 10*i, 160 - 10*i, 160 - 10*i);  // bottom
            g.drawLine( 10 + 10*i,   20 + 10*i,  10 + 10*i, 160 - 10*i);  // left
        }
    }
}

Exercise - answer, alternative version

import java.awt.*;

public class Spiral {
    public static void main(String[] args) {
        DrawingPanel panel = new DrawingPanel(170, 170);
        Graphics g = panel.getGraphics();
        int x = 0, y = 10;
        int len = 160;
        for (int i = 0; i < 8; i++) {
            g.drawLine(x, y, x + len, y);  // right
            x = x + len;
            len = len - 10;
            g.drawLine(x, y, x, y + len);  // down
            y = y + len;
            g.drawLine(x, y, x - len, y);  // left
            x = x - len;
            len = len - 10;
            g.drawLine(x, y, x, y - len);  // up
            y = y - len;
        }
    }
}