Groovy: Spread Operator (*.)

Spread (*.) operator is used to invoke an action on all items of an aggregate object.

def employees = [

         new Employee (firstName : "Menon", lastName : "Hari"),

         new Employee (firstName : "Bhat", lastName : "Srini"),

         new Employee (firstName : "Krishna", lastName : "Gurram")

]

Below statement return all the first names of the employees.

def firsNames = employees*.firstName

Below statement return all the last names of the employees.

def lastNames = employees*.lastName

Find the below working application.

HelloWorld.groovy

class Employee{
 String firstName
 String lastName
}

def employees = [
 new Employee (firstName : "Menon", lastName : "Hari"),
 new Employee (firstName : "Bhat", lastName : "Srini"),
 new Employee (firstName : "Krishna", lastName : "Gurram")
]

def firsNames = employees*.firstName
def lastNames = employees*.lastName

println "firstNames : ${firsNames}"
println "lastNames : ${lastNames}"

Output

firstNames : [Menon, Bhat, Krishna]
lastNames : [Hari, Srini, Gurram]

Is spread operator null safe?

Yes, spread operator is null safe, if any element in the collection is null, then it returns null instead of throwing NullPointerException.

HelloWorld.groovy

class Employee{
 String firstName
 String lastName
}

def employees = [
 null,
 new Employee (firstName : "Menon", lastName : "Hari"),
 null,
 new Employee (firstName : "Bhat", lastName : "Srini"),
 null,
 new Employee (firstName : "Krishna", lastName : "Gurram"),
 null
]

def firsNames = employees*.firstName
def lastNames = employees*.lastName

println "firstNames : ${firsNames}"
println "lastNames : ${lastNames}"

Output

firstNames : [null, Menon, null, Bhat, null, Krishna, null]
lastNames : [null, Hari, null, Srini, null, Gurram, null]

You can even perform operation on a list using *. Operator.

HelloWorld.groovy

evenNumbers = [0, 2, 4, 6, 8]

squaresOfEvenNumbers = evenNumbers*.multiply(2)
sumEveryNumBy2 = evenNumbers*.plus(2)

println "evenNumbers : $evenNumbers"
println "squaresOfEvenNumbers : $squaresOfEvenNumbers"
println "sumEveryNumBy2 : $sumEveryNumBy2"

Output

evenNumbers : [0, 2, 4, 6, 8]
squaresOfEvenNumbers : [0, 4, 8, 12, 16]
sumEveryNumBy2 : [2, 4, 6, 8, 10]

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