Combination or concatenation of two or multiple lists are believed to appear quite frequently in programming. This article aims to show you how to union two lists in Groovy in different ways.
Combine lists with addAll
The java.util.ArrayList.addAll(Collection<? extends E> c) method appends all of the elements from the specified collection (the second list) to the end of the current list (the first list), in the order that they are returned by the specified collection’s Iterator.
def fruits = ["Apple", "Banana", "Cherry"] def newFruits = ["Pear", "Plum", "Strawberry"] fruits.addAll(newFruits) println fruits
The output looks like the following
[Apple, Banana, Cherry, Pear, Plum, Strawberry]
Combine lists using the plus operator
Naturally we can think about the plus operator when combining two lists. The plus operator will return a new list containing all the elements of the two lists while and the addAll method appends the elements of the second list to the end of the first one.
def fruits = ["Apple", "Banana", "Cherry"] def newFruits = ["Pear", "Plum", "Strawberry"] println fruits + newFruits
Obviously, the output is the same as the one using addAll method.
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