iReport Ultimate Guide

iReport Ultimate Guide
it was still valid because the user was not using a new tag in the XML. With the move to an XML schema, the JRXML output
of iReport 3.1.1 and newer can only be compiled with a JasperReports 3.1.0 or later.
3.5 Expressions
Though I designed iReport to be useful for non-technical report designers, many settings in a report are defined using formulas
(such as conditions to hide an element, special calculations, text processing, and so on) that require a minimum knowledge of
a scripting language.
Fortunately, formulas can be written in at least three languages, two of which (JavaScript and Groovy) are pretty simple and
can be used without knowledge of programming methods.
All of the formulas in JasperReports are defined through expressions. The default expression language is Java, but I suggest
that you design your projects with JavaScript or Groovy. Both hide a lot of the Java complexity and are definitively the
languages to use if you don’t know Java. The language is a property of the document, so, to set it, select the document root
node in the Outline view and choose your language in the Language property in the Properties view. We will go through all
the languages in the following sections, but let’s concentrate for a moment on our definition of an “expression,” in particular
the type you will declare for it and why that is important in JasperReports.
An expression is just a formula that operates on some values and returns a result. Think of an expression as the formula you
might define for a spreadsheet cell. A cell can have a simple value or you can use a complex formula that refers to other
values; in a spreadsheet you would refer to values contained in other cells, whereas in JasperReports you will use the report
fields, parameters, and variables. The main point is that whatever you have in your expression, when it is computed it gives a
value as result (which can be null; that’s still a value).
3.5.1 The Type of an Expression
The type of an expression is the nature of the value resulting from it; the type is determined by the context in which the
expression is used. For example, if your expression is used to evaluate a condition, the type of the expression should be
Boolean (true or false); if you are creating an expression that should be displayed in a textfield, it will probably be a String or
a number (Integer or Double). We could simplify the declaration of types by limiting them to text, numbers, Booleans, and
generic object values. Unfortunately, JasperReports is a bit more formal and in many cases you have to be very precise when
setting the type of your expression.
So far, we are discussing only Java types (regardless of the language used). Some of the most important types are:
As noted, if the expression is used to determine the value of a condition that determines, for instance, whether an element
should be printed, the return type will be java.lang.Boolean; to create it, you need an expression that returns an instance of
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java.lang.Boolean Defines an Object that represents a boolean value such as true and
false
java.lang.Byte Defines an Object that represents a byte
java.lang.Short Defines an Object that represents an short integer
java.lang.Integer Defines an Object that represents integer numbers
java.lang.Long Defines an Object that represents long integer numbers
java.lang.Float Defines an Object that represents floating point numbers
java.lang.Double Defines an Object that represents real numbers
java.lang.String Defines an Object that represents a text
java.util.Date Defines an Object that represents a date or a timestamp
java.lang.Object A generic java Object