CHAPTER 14 ■ RECURSION
import javax.swing.JPanel;public class SierpinskiTrianglePanel extends JPanel {private static final long serialVersionUID = 1L;int maxLevel = 7;private void drawTriangle(int level, Graphics g, Point2D.Double point1,
Point2D.Double point2, Point2D.Double point3) {
if (level < maxLevel) {
// Work our way down through the levels
Point2D.Double midPoint1 = getMiddlePoint(point1, point2);
Point2D.Double midPoint2 = getMiddlePoint(point2, point3);
Point2D.Double midPoint3 = getMiddlePoint(point1, point3);g.setColor(new Color((int)(Math.random() * 0xFFFFFF)));drawTriangle(level + 1, g, point1, midPoint1, midPoint3);
drawTriangle(level + 1, g, midPoint1, point2, midPoint2);
drawTriangle(level + 1, g, midPoint3, midPoint2, point3);
} else {
// At the bottom level, draw the actual triangles
// (which are parts of the larger triangles)
int[] xPoints = {
new Double(point1.getX()).intValue(),
new Double(point2.getX()).intValue(),
new Double(point3.getX()).intValue()
};
int[] yPoints = {
new Double(point1.getY()).intValue(),
new Double(point2.getY()).intValue(),
new Double(point3.getY()).intValue()
};
g.fillPolygon(xPoints, yPoints, 3);
}
}private Point2D.Double getMiddlePoint(Point2D.Double point1,
Point2D.Double point2) {
double newX = (point1.getX() + point2.getX()) / 2;
double newY = (point1.getY() + point2.getY()) / 2;
return new Point2D.Double(newX, newY);
}public void paint (Graphics g) {
super.paintComponent(g);
int height = this.getHeight();
int width = this.getWidth();
// Here's one way to get the height of an equilateral triangle Double doubleHeight
= Math.sqrt(height * height - (width / 2) * (width / 2)); // 0 on the Y axis is at
the bottom, so this seems upside-down