[ GroovyGN ] Using the OrderBy Comparator

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The OrderBy class in Groovy implements the Comparator interface. We provide one or more closures to an OrderBy object, which are executed for comparing values. We can use this object whenever we need a comparator, for example if we invoke the sort() method on a collection.

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1. class Language {  
2.     String name  
3.     boolean dynamic  
4.     String toString() { "name: $name, dynamic: $dynamic" }  
5. }  
6.   
7. def languages = [  
8.     new Language(name: 'Groovy', dynamic: true),  
9.     new Language(name: 'Java', dynamic: false),  
10.     new Language(name: 'Clojure', dynamic: true)  
11. ]  
12.   
13. // We order first on dynamic property and then name property.  
14. def orderByDynamicAndName = new OrderBy([{ it.dynamic }, { it.name }])  
15. def sortedLanguages = languages.sort(orderByDynamicAndName)  
16.   
17. assert 'Java' == sortedLanguages[0].name  
18. assert !sortedLanguages[0].dynamic  
19. assert 'Clojure' == sortedLanguages[1].name  
20. assert 'Groovy' == sortedLanguages[2].name  
21. assert sortedLanguages[1].dynamic && sortedLanguages[2].dynamic  

Another simple example:

groovy:000> class P{String name; int age; String toString(){"name:$name, age:$age"}}
===> true
groovy:000> people = [new P(name:"John",age:37), new P(name:"Mark",age:16)]
===> [name:John, age:37, name:Mark, age:16]
groovy:000> orderByName = new OrderBy([{it.name}])
===> groovy.util.OrderBy@54eb2b70
groovy:000> orderByAge = new OrderBy([{it.age}])
===> groovy.util.OrderBy@60410cd
groovy:000> people.sort(orderByName)
===> null
groovy:000> people
===> [name:John, age:37, name:Mark, age:16]
groovy:000> people.sort(orderByAge)
===> null
groovy:000> people
===> [name:Mark, age:16, name:John, age:37]