Circular Motion Direction Detection

CircleDetector.java

import java.awt.*;
import java.awt.event.*;

public class CircleDetector extends Frame implements MouseMotionListener {
	
	private Label direction = null;
	
	// These two variables help us detect the direction and circular motion.
	private double lastAngle = 0;
	private boolean antiClockwise = true;
	
	public static void main(String[] args) {
		new CircleDetector();
	}
	
	public CircleDetector() {
		super( "Circle Detector" );
		this.setSize( 300, 300 );
		
		this.direction = new Label("Anti Clockwise");
		this.add( this.direction );
		
		this.addMouseMotionListener( this );
		
		this.setVisible(true);
	}
	
	/*!
	Mouse Motion Events
	 */
	public void mouseMoved( MouseEvent e ) {}
	
 	public void mouseDragged( MouseEvent e ) {
		// Work out the current angle - first we work out the length of the line
		// between two points. The window is locked at 300 by 300, so fix the point
		// at 150, 150.
		double dx = 150.0 - e.getX();
		double dy = 150.0 - e.getY();
		
		// Now we can work out the arctanget of the line. This is given in radians.
		double angle = Math.atan2( dy, dx );
		
		// Now check against the last angle and see what is happening.
		if ( this.lastAngle < angle ) {
			// We're going clockwise
			this.direction.setText("Clockwise");
		}
		else if ( this.lastAngle > angle ) {
			// We're going anti clockwise.
			this.direction.setText("Anti Clockwise");
		}
		else {
			// We're somehow standing still, yet moving.
			// This can happen if the mouse is moving in a straight line to the center point.
			this.direction.setText("Undefined");
		}
		
		this.lastAngle = angle;
	}
	
	
}