Lists
Lists are data types that can hold multiple values of a certain type.
Lists are dynamically sized. So that means if we create a list of 0 length, we can still add elements to it.
There are multiple ways to create lists. The elements of a list are ordered, so the order won't change randomly.
// most simple list, size = 0
// the type is always ArrayList
def simpleList = []
def list = new ArrayList() // this is the same as above
def anotherList = ['He', 'llo', ' w', 'or', 'ld!'] // we can put values into the list, all of the same typeGetting values
Elements of a list can be accessed via get or the [] operator. You can also use the safe index operator ?[] to try to get the value while avoiding a NullPointerException.
Lists index start at 0.
def list = [9, 8, 7, 6, 5, 4, 3, 2, 1]
println(list[0]) // 9
println(list.get(0)) // 9
println(list[3]) // prints the 4th element: 6
println(list[-1]) // prints the last element: 1
println(list[-2]) // prints the 2nd last element: 2You can also get a range of elements by using the .. operator.
def list = [9, 8, 7, 6, 5, 4, 3, 2, 1]
def subList = list[2..5] // [7, 6, 5, 4]
// reversing the indexes results in a reversed list
def subLis2 = list[5..2] // [4, 5, 6, 7]
// -1 is greater because it refers to the last elements, so its not reversed
def subList3 = list[2..-1] // [7, 6, 5, 4, 3, 2, 1]Modifying lists
Lists can be modified by using set(), add() and remove(). We can also use the [] and << operators
def list = []
list.add(1) // adds 1 to the lest
// list is now [1]
list << 3 // adds 3 to the list
list << 9
// [1, 3, 9]
list.set(1, 5) // sets the element at index 1 to 5
list[1] = 5 // same thing as above
// [1, 5, 9]
list.remove(0) // removes the first element
// [5, 9]Spread Operator
Using the Spread Operator you can call methods or access fields on an all objects inside a list.
class Demo {
def value
}
def list = [new Demo(value: 1), new Demo(value: 2), new Demo(value: 4), new Demo(value: 8)]
def values = list*.value // gets the value field of each Demo object in the list
// [1, 2, 4, 8]A similar mechanism can be used to spread the elements of a list across multiple parameters of a function.
def f(a, b, c, d) {
(a + b) * (c + d)
}
def list = [1, 2, 4, 8]
def value = f(*list) // spread the list into the valid arguments
// 36Or to spread the elements of a list across another list.
def list = [1, 2, 4, 8]
def newList = [0, *list, 16]
// [0, 1, 2, 4, 8, 16]
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