<p>As the JavaDoc states, DateFormats are inherently unsafe for multithreaded use. 
Sharing a single instance across thread boundaries without proper synchronization will result in erratic behavior of the
application.</p>
<p>You may also experience serialization problems.</p>
<p>Using an instance field is recommended.</p>
<p>For more information on this see <a href="http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=6231579">Sun Bug #6231579</a>
and <a href="http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=6178997">Sun Bug #6178997</a>.</p>