title: Object constructor not called when parsed from json string
body: <p>Why is <code>IACircle</code> constructor not called?<br/>
  This is how I load the Json ..</p>
  
  <pre><code>BufferedReader br = new BufferedReader(in);
  LevelDefinition ld = new Gson().fromJson(br, LevelDefinition.class);
  </code></pre>
  
  <p>Json string ..</p>
  
  <pre><code>{
      "iaCircles": [
          {
              "x": -32.0,
              "y": -5.0,
              "angle": 0.0,
              "radius": 2.5,
              "density": 0.0,
              "friction": 0.0,
              "restitution": 1.0,
              "textureSelection": "CIRCLE",
              "inflictsDamage": true,
              "fixedRotation":true
          },
          {
              "x": 55.0,
              "y": -5.0,
              "angle": 0.0,
              "radius": 2.5,
              "density": 0.0,
              "friction": 0.0,
              "restitution": 1.0,
              "textureSelection": "CIRCLE",
              "inflictsDamage": true,
              "fixedRotation":true
          }
      ]
  }
  </code></pre>
  
  <p>Java class parsed into ..</p>
  
  <pre><code>public class LevelDefinition {
  
      private Vector&lt;IACircle&gt; iaCircles;
  }
  </code></pre>
  
  <p><code>IACircle</code> definition ..</p>
  
  <pre><code>public class IACircle {
      public IACircle (
          float x, float y, float angle, float radius,
          float density, float friction, float restitution,
          String textureSelection, boolean inflictsDamage, boolean fixedRotation) { 
          System.out.println("constructor called, circle");
      }
  }
  </code></pre>