Over a million developers have joined DZone.

Groovy Goodness: Using Tuples

Learn all about using tuples, which are ordered, immutable elements lists, in Groovy.

· Java Zone

What every Java engineer should know about microservices: Reactive Microservices Architecture.  Brought to you in partnership with Lightbend.

A tuple is an ordered, immutable list of elements. Groovy has its own groovy.lang.Tuple class. We can create an instance of a Tuple by providing all elements that need to be in the Tuple via the constructor. We cannot add new elements to a Tuple instance or remove elements. We cannot even change elements in a tuple, so it is completely immutable. This makes it very usable as the return value for a method where we need to return multiple values. Groovy also provides a Tuple2 class that can be used for tuple instance of only two elements. The elements are typed in a Tuple2 instance.

In the following example we see different uses of the Tuple and Tuple2 classes:

def tuple = new Tuple('one', 1, new Expando(number: 1))

assert tuple.size() == 3

// To get the value of an element
// at a certain position we use
// the get(index) method.
assert tuple.get(0) == 'one'

// We can use the [] syntax to
// get elements from the tuple.
assert tuple[1] == 1

// We can use methods added to the
// Collection API by Groovy.
assert tuple.last().number == 1

// We cannot change the tuple.
try {
    assert false
} catch (UnsupportedOperationException e) {
    assert e

try {
    assert false
} catch (UnsupportedOperationException e) {
    assert e

try {
    tuple[0] = 'new value'
    assert false
} catch (UnsupportedOperationException e) {
    assert e

// Create a Tuple with fixed size 
// of 2 elements, a pair.
def pair = new Tuple2('two', 2)

// The Tuple2 class has extra methods
// getFirst() and getSecond() to 
// access the values.
assert pair.first == 'two'
assert pair.second == 2

An example of how to use a Tuple2 as return value for a method:

def calculate(String key, Integer... values) {
    // Method return a Tuple2 instance.
    new Tuple2(key, values.sum())

// Use multiple assignment to
// extract the values from the tuple.
// Tuple2 has typed objects.
def (String a, Integer b) = calculate('sum', 1, 2, 3)

assert a == 'sum'
assert b == 6

Written with Groovy 2.4.6.

Microservices for Java, explained. Revitalize your legacy systems (and your career) with Reactive Microservices Architecture, a free O'Reilly book. Brought to you in partnership with Lightbend.


Published at DZone with permission of Hubert Klein Ikkink, DZone MVB. See the original article here.

Opinions expressed by DZone contributors are their own.

The best of DZone straight to your inbox.

Please provide a valid email address.

Thanks for subscribing!

Awesome! Check your inbox to verify your email so you can start receiving the latest in tech news and resources.

{{ parent.title || parent.header.title}}

{{ parent.tldr }}

{{ parent.urlSource.name }}