// demonstrates use of recursion graphically

import java.awt.*;
import javax.swing.JApplet;

public class LineRecursion extends JApplet {
	
	private static final long serialVersionUID = 1L;
	private final int APPLET_WIDTH = 640;
	private final int APPLET_HEIGHT = 320;
	private final int MIN_HEIGHT = 15;  // smallest bar height
	private final int BAR_WIDTH = 5;
	private static final Color[ ] choices = new Color[ ] 
	            {Color.blue, Color.red,  Color.orange, Color.cyan};
	
	/*
	 * sets the window size
	 */
	public void init( ) {
		setSize(APPLET_WIDTH, APPLET_HEIGHT);
	}

	/*
	 * returns next color in sequence
	 */
	public int nextColor(int index) {
		index++;
		if (index >= choices.length) {
			index = 0;
		}
		return index;
	}
	
	/*
	 * draws a rectangle, then calls itself recursively
	 */
	public void drawLines(Graphics page, int loc, int colorChoice, int height) {		
		page.setColor(choices[colorChoice]);
		page.fillRect(loc, 0, BAR_WIDTH, height);
		if (height > MIN_HEIGHT) {
			drawLines(page, loc - height/2, nextColor(colorChoice), height/2);
			drawLines(page, loc + height/2, nextColor(colorChoice), height/2);
		}
	}
	
	/*
	 * perform the initial call to the drawPictures method
	 */
	public void paint (Graphics page) {

		drawLines(page, APPLET_WIDTH/2, 0, APPLET_WIDTH/2);
	}

}