error changing orientation x-Axis label

[mmm286]

Hi,
Congratulations for these wonderfoul software.
I'm trying to rotate to put in vertical mode my label of x-Axis. I put in the code:

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				XYPlot plot = chart.getXYPlot();
				ValueAxis axis = plot.getRangeAxis();
				axis.setLabelAngle(Math.PI / 2.0);

But it says me:

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Exception in thread "Thread-12" java.lang.ClassCastException: org.jfree.chart.plot.CategoryPlot cannot be cast to org.jfree.chart.plot.XYPlot
	at org.jfree.chart.JFreeChart.getXYPlot(JFreeChart.java:857)
	at tercera.mostrarTercera(tercera.java:131)
	at UI$4.run(UI.java:484)
	at java.lang.Thread.run(Unknown Source)

Could you help me please?
Thanks and sorry for my english!