A class annotation used to make a class Comparable by (potentially) multiple Comparators. As an example, given this class:

@Sortable class Person {
    String first
    String last
    Integer born
}

The generated Groovy class will:

• implement the Comparable interface
• have a compareTo method based on the first, last and born properties (priority ordering will be according to the ordering of property definition, highest first, unless 'includes' is used; in which case, priority will be according to the order given in the includes list)
• have three Comparator methods named comparatorByFirst, comparatorByLast and comparatorByBorn
• sort by natural order by default, reversed natural order can be specified

The properties within the class must themselves be Comparable or @Sortable.

More examples:

//--------------------------------------------------------------------------
import groovy.transform.Sortable
import groovy.transform.ToString

@Sortable
@ToString
class Course {
    // Order of properties determines priority when sorting
    String title
    Date beginDate
    Integer maxAttendees  // int doesn't implement Comparable, so use Integer
}


final Course groovy = new Course(
        title: 'Groovy', beginDate: new Date() + 7, maxAttendees: 40)
final Course groovy2 = new Course(
        title: 'Groovy', beginDate: new Date() + 2, maxAttendees: 50)
final Course grails = new Course(
        title: 'Grails', beginDate: new Date() + 1, maxAttendees: 20)


final List<Course> courses = [groovy, groovy2, grails]
assert courses.last().title == 'Grails'

// Use toSorted() method to sort
final List<Course> sorted = courses.toSorted()

assert sorted.first().title == 'Grails'
assert sorted.last().title == 'Groovy'
assert sorted.maxAttendees == [20, 50, 40]

//--------------------------------------------------------------------------
// Order of fields for includes determines priority when sorting
import groovy.transform.Sortable
import groovy.transform.ToString

@Sortable(includes = ['title', 'maxAttendees'])
// Or @Sortable(excludes = ['beginDate'])
@ToString
class Course {
    String title
    Date beginDate
    Integer maxAttendees
}

final Course groovy = new Course(
        title: 'Groovy', beginDate: new Date() + 7, maxAttendees: 40)
final Course groovy2 = new Course(
        title: 'Groovy', beginDate: new Date() + 2, maxAttendees: 50)
final Course grails = new Course(
        title: 'Grails', beginDate: new Date() + 1, maxAttendees: 20)


final List<Course> courses = [groovy, groovy2, grails]

// Use toSorted() method to sort
final List<Course> sorted = courses.toSorted()

assert sorted.first().title == 'Grails'
assert sorted.last().title == 'Groovy'
assert sorted.maxAttendees == [20, 40, 50]

//--------------------------------------------------------------------------
// Static methods to create comparators.
final Comparator byMaxAttendees = Course.comparatorByMaxAttendees()
final List<Course> sortedByMaxAttendees = courses.sort(false, byMaxAttendees)

assert sortedByMaxAttendees.maxAttendees == [20, 40, 50]
// beginDate is not used for sorting
assert sortedByMaxAttendees[2].beginDate < sortedByMaxAttendees[1].beginDate

assert Course.declaredMethods.name.findAll { it.startsWith('comparatorBy') }.toSorted() == ['comparatorByMaxAttendees', 'comparatorByTitle']

//--------------------------------------------------------------------------
// Sorting by max attendees using reversed order
import groovy.transform.Sortable
import groovy.transform.ToString

@Sortable(includes = ['points'], reversed = true)
@ToString
class LeaderBoardEntry {
    String team
    int points
}


final LeaderBoardEntry teamA = new LeaderBoardEntry(team: "Team A", points: 30)
final LeaderBoardEntry teamB = new LeaderBoardEntry(team: "Team B", points: 80)
final LeaderBoardEntry teamC = new LeaderBoardEntry(team: "Team C", points: 50)

final List<LeaderBoardEntry> leaderBoard = [teamA, teamB, teamC].toSorted()

assert leaderBoard.first().team == 'Team B'
assert leaderBoard.last().team == 'Team A'
assert leaderBoard.points == [80, 50, 30]