Strings and GStrings

Groovy has several ways to write text. The two you'll use most: single quotes for plain strings and double quotes for GStrings — strings with ${} placeholders.

def name = 'Ada'
def age = 36
def book = [title: 'Dune']

println 'Hello, $name'                 // single quotes: no interpolation
println "Hello, $name"                 // $variable
println "Next year: ${age + 1}"        // ${expression}
println "Upper: ${name.toUpperCase()}"
println "Book: $book.title"           // $a.b works for properties
println "Price: \$5"                   // escape a literal dollar

Hello, $name
Hello, Ada
Next year: 37
Upper: ADA
Book: Dune
Price: $5

• $name inserts a variable; ${ ... } inserts any expression.
• $book.title reads the property title — but $name.size() would not call the method; use ${name.size()} for method calls.
• Single-quoted strings are plain java.lang.Strings.

Multi-line strings

def user = 'ada'
def email = """\
    Hi $user,
    Your report is ready.
    — The Team""".stripIndent()
println email

def sql = '''
SELECT *
FROM users
'''.trim()
println sql

Hi ada,
Your report is ready.
— The Team
SELECT *
FROM users

Triple quotes (''' plain, """ with placeholders) span lines. The backslash after the opening quotes skips the first new line, and stripIndent() removes the common leading spaces.

Slashy strings

def path = /C:\Users\ada\notes.txt/
println path
def pattern = /\d{3}-\d{4}/
println '555-1234' ==~ pattern

C:\Users\ada\notes.txt
true

Between slashes, backslashes are literal — ideal for regular expressions and Windows paths. (==~ tests a regex match; Level 2 covers regexes.)

Concatenation and repetition

println 'Groovy' + ' ' + 'rocks'
println '-' * 20
println 'abc' + 1 + 2
println 1 + 2 + 'abc'

Groovy rocks
--------------------
abc12
3abc

+ joins strings, * repeats them. Evaluation goes left to right, so 1 + 2 + 'abc' adds the numbers first.

GString gotcha

def key = "id"
def gkey = "${key}"
println 'id' == gkey
println gkey.class.simpleName
def map = [(gkey.toString()): 1]
println map['id']

true
GStringImpl
1

A GString compares equal to a String with ==, but it's a different class with a different hash code — so don't use GStrings as map keys. Call toString() first, or use single-quoted strings.