title: Sort ArrayList<Object> by date that contains two different Object Classes
body: <p>I have two Model classes that I am adding to ArrayList items and both of the model classes have a getDate() and I want to sort the list by date. I have been going at it for a while but can't seem to get it. </p>
  
  <pre><code>    ArrayList&lt;Object&gt; items = new ArrayList&lt;&gt;();
      ArrayList&lt;LiftDate&gt; liftDates = LiftDateHandler.get(getActivity()).getDate();
      ArrayList&lt;OneRepMax&gt; oneRepMaxes = OneRepMaxHandler.get(getActivity()).getORM();
      items.addAll(liftDates);
      items.addAll(oneRepMaxes);
  </code></pre>
  
  <p>Both LiftDate.class and OneRepMax.class contain:</p>
  
  <pre><code>public Date getDate() {
      return mDate;
  }
  </code></pre>
  
  <p>How do I sort the ArrayList items based on the two Objects getDate()? </p>