Why add Groovy to Java? - Making Java Groovy - page 10

Next, I sort the strings using the two-argument version of Collections.sort . The in-
teresting part is that the second argument to the sort method is a closure (between the
braces), which is then “coerced” to implement Comparable using the as operator. [ 3 ]
3 Closure coercion like this is discussed further in chapter 4 .
The closure is intended to be the implementation of the compare(String,String)
method analogous to that shown in the previous Java listing. Here I show the two dummy
arguments, s1 and s2 ,totheleftofthearrow,andthenusethemontherightside.Iprovide
the closure as the implementation of the Comparator interface. If the interface had sev-
eral methods and I wanted to supply different implementations for each method, I would
provide a map with the names of the methods as the keys and the corresponding closures
as the values.
Finally,Iusetheso-called spread-dotoperatortoinvokethe size methodoneachelement
of the sorted collection, which returns a list of results. In this case I'm asking for the length
of each string in the collection and comparing the results to the expected values.
Bytheway,theGroovyscriptdidn'trequireanyimports,either.Javaautomatically imports
the java.lang package. Groovy also automatically brings in java.util , java.net ,
java.io , groovy.lang , groovy.util , java.math.BigInteger , and java
.math.BigDecimal . It's a small thing, but convenient.
Groovy Feature
Native syntax for collections and additional automatic imports reduces both the amount of
required code and its complexity.
If you've used Groovy before you probably know that there's actually an even simpler way
to do the sort. I don't need to use the Collections class at all. Instead, Groovy has
added a sort method to java.util.Collection itself. The default version does a
natural sort, and a one-argument version takes a closure to do the sorting. In other words,
the entire sort can be reduced to a single line:
strings.sort { -it?.size() }