title: ProvidesKey<T> in GWT
body: <p>In GWT documentation in <a href="http://code.google.com/webtoolkit/doc/latest/DevGuideUiCellWidgets.html#Selection_Data_Paging" rel="nofollow">this</a> article in "Keys" section said that <code>ProvidesKey&lt;T&gt;</code> allow us to identify the DTO object in cell list or cell table. Also there is a code sample that demonstrate that(they modify the contact and says that selection remains on that contact because they have provided a <code>keyProvider</code>). </p>
  
  <pre><code>Contact sarah = CONTACTS.get(3);
      selectionModel.setSelected(sarah, true);
  
      // Modify the name of the contact.
      sarah.name = "Sara";
  </code></pre>
  
  <p>But it also works without <code>keyprovider</code>. So the question is for what purposes we use <code>ProvidesKey</code> interface and why? At that example we can do the same without it.</p>