Building and testing web applications - Making Java Groovy - page 348

and the this reference refers to the object where the category is invoked. The analogous
implementation for the currency category is
import java.text.NumberFormat
@Category(Number)
class AnnotationCurrencyCategory {
String asCurrency() {
NumberFormat.currencyInstance.format(this)
}
String asCurrency(Locale loc) {
NumberFormat.getCurrencyInstance(loc).format(this)
}
}
Number.mixin AnnotationCurrencyCategory
def amount = 1234567.89012
println amount.asCurrency()
println amount.asCurrency(Locale.GERMANY)
println amount.asCurrency(new Locale('hin','IN'))
Note also the use of the mixin method to add the category to the Number class.
Presumably, if the ServletCategory was being implemented now, it would use the an-
notation approach. The result is the same either way, of course. [ 1 ]
1 The topic source code includes the two ways of doing the currency category as well as a test case.
An example will make this clear. The next listing shows a class called HelloName-Ser-
vlet , implemented in Groovy, which receives a name parameter and replies with the
standard welcome.