Variables and def

A variable names a value so you can use it later. Groovy lets you declare it with def (no type), with var (same as def in dynamic code), or with a type, as in Java.

def city = 'Lagos'
int temperature = 24
String unit = 'degrees'
println "It is $temperature $unit in $city"

temperature = 27
temperature += 1
temperature++
println temperature

def (a, b) = [1, 2]
println "a=$a b=$b"
(a, b) = [b, a]
println "a=$a b=$b"

It is 24 degrees in Lagos
29
a=1 b=2
a=2 b=1

• def name = value creates a variable whose type can change.
• int, String, and other Java types make the intent clear and, with static compilation, are checked by the compiler.
• +=, -=, ++, and -- work as in Java.
• Multiple assignment: def (a, b) = [1, 2] unpacks a list; (a, b) = [b, a] swaps two values.

Typed variables convert or complain

int count = 3
count = 4.9          // a decimal is narrowed to an int
println count

def anything = 3
anything = 'now a string'
println anything

try {
    int n = 'five'
} catch (e) {
    println e.class.simpleName
}

4
now a string
GroovyCastException

A def variable accepts any value. A typed variable converts numbers to its type but refuses values that can't be converted (here with a GroovyCastException at runtime).

final and val

final rate = 0.2
val limit = 10       // Groovy 6: same as final
println rate * limit

2.0

final (or val, new in Groovy 6) prevents reassignment. Use it for values that shouldn't change — reassigning is a compile error.

Naming

• Names can contain letters, digits, _, and $, and can't start with a digit. They're case-sensitive.
• Convention: camelCase for variables and methods, PascalCase for classes, UPPER_SNAKE_CASE for constants.

Practice

Store a product name and a price in variables and print Coffee costs 3.50.

def product = 'Coffee'
def price = 3.50
println "$product costs $price"

Coffee costs 3.50