The membership operator (in) can be used to test whether provided value is in the target collection or not. It's equivalent to calling contains() method.

Examples

src/Example1MembershipOpt.groovy

def numbers = [2,4,6,8]
println 2 in numbers
println 3 in numbers

println numbers.contains(2)

Output

true
false
true

The membership operator can be used for maps as well:

src/Example2MembershipOptForMap.groovy

def numbers = [two: 2, four: 4, six: 6, Eight: 8]
println 'two' in numbers
println 2 in numbers

Output

true
false

In fact the membership operator can be used with any object which defines boolean inCase(.....) method. Let's create our own object with this method:

src/Example3MembershipOptCustom.groovy

class Multiple{
 int num;
    Multiple(int num) {
        this.num = num
    }

    boolean isCase(otherNum){
     return otherNum % num == 0
 }
}

def multipleOfThree = new Multiple(3);
println 6 in multipleOfThree
println 7 in multipleOfThree

Output

true
false

Example Project

Dependencies and Technologies Used:

• Groovy 2.5.5
• JDK 9.0.1