title: Rotating a point around a center point, something wrong
body: <p>in a current assignment we need to create a method, to rotate a given point, around
  a center point given, in the angle given, in CLOCK WISED offset.
  after searching through posts here, i thought i figured it out, but according to my 
  teacher, something is wrong with this and i can't figure it out.</p>
  
  <p>i was hoping maybe someone could help out pointing what the problem is.</p>
  
  <p>this is my method</p>
  
  <pre><code>    /**
   * rotate this Point around a given enter point, with the given angle, in clock wised offset.
   * @param center - the center Point for rotation
   * @param angle - the size angle in degrees - to be rotate clock wised
   */
  public void rotate(Point center, double angle){
  
      // convert the angle to radiant (to use with Math class methods). The negative sign is because, in trigonometry, default rotation is COUNTER-clock wised.
      double rad_angle = -Math.toRadians(angle); 
  
      // in order to rotate properly, we need to know the difference between the coordinates, to get a base for the rotation.
      double diff_x = this.x - center.X(); 
      double diff_y = this.y - center.Y(); 
  
      // calculate the rotation difference
      this.x = diff_x * Math.cos(rad_angle) - diff_y* Math.sin(rad_angle);  
      this.y = diff_x * Math.sin(rad_angle) + diff_y * Math.cos(rad_angle);
  
      // translate the differences back to this point
      this.x = this.x + center.X(); 
      this.y = this.y + center.Y();
  
      return;
  }//rotate
  </code></pre>
  
  <p>thanks in advance.</p>