title: Does Collections.unmodifiableCollection(list) copy the collection?
body: <pre><code>private List list;
  </code></pre>
  
  <p>If we use <code>Collections.unmodifiableCollection(list)</code>, will this return a copy of the collection, or is it faster than creating a copy? We could do <code>other.addAll(list)</code> but we have list of 600,000 object, so <code>addAll</code> is not so good.</p>
  
  <p>Caller just needs a read-only collection.</p>