Operators

Groovy has Java's operators, plus several that remove whole lines of boilerplate.

Comparison: == means equals

def a = new String('hi')
def b = new String('hi')

println a == b            // value equality (calls equals)
println a.is(b)           // identity: the same object?
println a === b           // identity operator (Groovy 3+)
println 3 <=> 5           // spaceship: -1, 0, or 1
println 'b' <=> 'a'
println 2 in [1, 2, 3]

true
false
false
-1
1
true

In Java, == compares object references, a classic source of bugs with strings. In Groovy, == compares values (it calls equals, or compareTo for comparable types). Use is() or === for identity.

Logical operators

def age = 20
def member = false
println age >= 18 && !member
println age < 13 || member

true
false

&& and || short-circuit: the right side runs only when needed.

Null-safe navigation and Elvis

def user = [name: 'Ada', address: null]

println user.address?.city          // null instead of an exception
println user.nickname ?: 'no nickname'
def city = user.address?.city ?: 'unknown'
println city

def title = null
title ?= 'Untitled'                 // assign only if null/false
println title

null
no nickname
unknown
Untitled

• ?. stops and returns null if the left side is null.
• ?: (the Elvis operator) returns the left side if it's "truthy", otherwise the right side — perfect for defaults.
• ?= assigns only when the variable is null or false (Groovy 5+).

Spread, ternary, and safe index

def people = [[name: 'Ada', age: 36], [name: 'Linus', age: 28]]
println people*.name                // spread: call on each element

def n = 7
println n % 2 == 0 ? 'even' : 'odd'

def list = null
println list?[0]                    // safe index (Groovy 3+)

[Ada, Linus]
odd
null

*. applies a property or method to every item of a list and collects the results — people*.name is short for people.collect { it.name }.

Common mistakes

• Using .equals everywhere out of Java habit — == already does it, and it's null-safe.
• Writing x ?: default when x may legitimately be 0 or '': those are "falsy" too (next lesson), so the default wins. Use x != null ? x : default if zero is a valid value.