title: Handling arraylist of arraylists with each having different objects
body: <p>I have this, three different array lists:</p>
  <pre><code>ArrayList&lt;type1&gt; alista = new ArrayList&lt;&gt;();
  ArrayList&lt;type2&gt; blistb = new ArrayList&lt;&gt;();
  ArrayList&lt;type3&gt; clistc = new ArrayList&lt;&gt;();
  </code></pre>
  <p>I then create a new array list and put those 3 array lists into it:</p>
  <pre><code>ArrayList&lt;Object&gt; all_lists = new ArrayList&lt;Object&gt;();
  all_lists.add(alista);
  all_lists.add(blistb);
  all_lists.add(clistc);
  </code></pre>
  <p>How do I add or remove objects inside all_lists: alista, blistb and clistc? I want to pass this all_lists back and forth between my methods inside my main(). I know doing it this way is probably wrong but I'd like to get this to work before I fix that with doing it better.</p>
  <p>For example how do I get blistb out of that, then add one type of type2 I've created and then remove one type2 (from blistb). And then put it back (or create new all_lists?) into all_lists?</p>