title: Compare two list objects
body: <p>I have two list as below:</p>
  
  <pre><code>List&lt;Category&gt; categories;
  List&lt;Category&gt; selectedCategories;
  </code></pre>
  
  <p>and model of Category:</p>
  
  <pre><code>(id,catTitle,catId)  
  </code></pre>
  
  <p>but I want to compare two list when:</p>
  
  <pre><code>selectedCategories:[{id=3, catTitle='first', catId=17},{id=4, catTitle='second', catId=18}]
  categories: [{id=null, catTitle='first', catId=17}
  </code></pre>
  
  <p>and get {id=3,catTitle='first',catId=17}</p>
  
  <p>but when id is null how to have {id=3,catTitle='first',catId=17} as result?!!!</p>