title: box2d contact listener fixtures order
body: <p>I am trying to understand how does it work.</p>
  
  <p>In my game I use box2d physics, to handle contacts I use contact listener, example:</p>
  
  <pre><code>ContactListener contactListener = new ContactListener()
  {
      @Override
      public void beginContact(Contact contact)
      {
          final Fixture x1 = contact.getFixtureA();
          final Fixture x2 = contact.getFixtureB(); 
  
          if (x1.getBody().getUserData() != null &amp;&amp; x2.getBody().getUserData() != null)
          {                   
              if (x1.getBody().getUserData().equals("player"))
              {                                               
                  player.increaseFootContacts();
              }
          }
      }
  </code></pre>
  
  <p>And here`s question, is there any order in those fixtures? (x1 or x2) after 2 test, I found out that in this case, my player will be x1, and other objects x2, should I also check reverse order ? (if x2 is player and so on) ? </p>