Writing methods in jasper report?

I am creating a jasper report.In that I want to write one method which takes integer and does some process and returns a string.I dont know how to write methods in jasper report.Is it possible to write?Can any one help me in this

I am using iReport3.6.0.

Sample code :

 <textField>
  <reportElement x="400" y="10" width="80" height="15"/>
  <textElement textAlignment="Left" verticalAlignment="Middle"/>
  <textFieldExpression     class="java.lang.String">
               <![CDATA[$F{intValue}]]>
  </textFieldExpression>
 </textField>

In the above code "$F{intValue}" returns integer.I want pass that to one method and that methods return type wants to be string.

Thanks