title: Comparing two ArrayLists and remove duplicates from original ArrayList
body: <p>I have two Custom <code>Arraylist</code>:</p>
  
  <pre><code>List&lt;Item&gt; before = new ArrayList&lt;Item&gt;();
  List&lt;ItemEx&gt; after = new ArrayList&lt;ItemEx&gt;();
  
  before.add(new Item(1L,"test1"));
  before.add(new Item(2L,"test2"));
  before.add(new Item(3L,"test3"));
  
  after.add(new ItemEx(1L,"test4"));
  after.add(new ItemEx(2L,"test5"));
  after.add(new ItemEx(4L,"test6")); 
  after.add(new ItemEx(5L,"test7")); 
  </code></pre>
  
  <p>I want to store the elements in the <code>List&lt;ItemEx&gt; after</code> and the element shoulds be after the removing of common element is <code>{3L, 4L, 5L}</code>.</p>