title: JFreeChart create tooltip in ChartPanel
body: <p>How can I generate a tooltip on chart mouse over in <code>JFreeChart</code>?
  I tried this:</p>
  
  <pre><code>chartPanel.setToolTipText("this is the string");
  </code></pre>
  
  <p>but this does not work. Am I supposed to do something else before? Something like this:</p>
  
  <pre><code>chartPanel.createToolTip().
  </code></pre>
  
  <p>I am calling these methods in the <code>chartMouseMoved</code> event.</p>