title: Rotation problems with Vector2 class
body: <p>I used <code>Vector2</code> class and did some rotation processes with it. But the results weren't what I expected. And I don't know what the problems are. Look at my code and outputs.</p>
  
  <pre><code>Vector2 vec;
  
  vec = new Vector2(5, 0);
  vec.setAngle(90.0f);
  // I expected output to be "x = 0"
  // But it prints "x = -2.1855695E-7" This is problematic.
  System.out.println("x = " + vec.x);
  // I expected output to be "y = 5"
  // And it prints "y = 5" OK. No problem.
  System.out.println("y = " + vec.y);
  
  vec = new Vector2(5, 0);
  vec.setAngle(180.0f);
  // I expected output to be "x = -5"
  // And it prints "x = -5" OK. No problem.
  System.out.println("x = " + vec.x);
  // I expected output to be "y = 0"
  // But it prints "y = -4.371139E-7" This is problematic.
  System.out.println("y = " + vec.y);
  
  vec = new Vector2(5, 0);
  vec.setAngle(270.0f);
  // I expected output to be "x = 0"
  // But it prints "x = 5.9624405E-8" This is problematic.
  System.out.println("x = " + vec.x);
  // I expected output to be "y = -5"
  // And it prints "y = -5" OK. No problem.
  System.out.println("y = " + vec.y);
  
  vec = new Vector2(5, 0);
  vec.setAngle(360.0f);
  // I expected output to be "x = 5"
  // And it prints "x = 5" OK. No problem.
  System.out.println("x = " + vec.x);
  // I expected output to be "y = 0"
  // But it prints "y = 8.742278E-7" This is problematic.
  System.out.println("y = " + vec.y);
  </code></pre>
  
  <p>Why some outputs aren't what I expected? Is it bad idea to use <code>Vector2</code> class for rotation processes ?</p>