Report variables

When we wrote the report in the Report Expressions section, we had to type the following expression twice:

$F{fixed_wing_single_engine_cnt}.intValue() +$F{fixed_wing_multiple_engine_cnt}.intValue())

This expression was typed once to calculate the number of fixed-wing aircraft reported, and again to calculate the total number of aircraft reported. This duplication is not a good thing because, if we need to change the expression for any reason, we would have to do it twice. JasperReports allows us to assign report expressions to a variable, eliminating the need to type the expression multiple times. The following JRXML template is a modified version of the one we wrote in that section, this version takes advantage of report variables to eliminate the duplicate expression.

<?xml version="1.0" encoding="UTF-8"  ?>
<jasperReportxmlns="http://jasperreports.sourceforge.net/jasperreports"xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
              xsi:schemaLocation...