Kotlin - 创建一个指定长度的随机整数的 ArrayList？

Question

I have an ArrayList like this :

var amplititudes : ArrayList<Int> = ArrayList()

I want to populate this with random Ints. How can I do this?

Answer 1

One option is to use the array constructor as following:

var amplititudes  = IntArray(10) { Random().nextInt() }.asList()

Another strategy is:

var amplititudes  = (1..10).map { Random().nextInt() }

EDIT

As suggested in the comment instead of creating an instance of Random each time it is better to initialize it once:

var ran = Random()
var amplititudes  = (1..10).map { ran.nextInt() }

Answer 2

Based to the answer of @Md Johirul Islam You can also use :

val from = 0
val to = 11
var random = Random()
var amplititudes  = IntArray(10) { random.nextInt(to - from) +  from }.asList()

in this solution you can specify the range of ints that you want, from 0 to 10 for example

Answer 3

Maybe something like this:

val amplitudes = ThreadLocalRandom.current().let { rnd ->
    IntArray(5) { rnd.nextInt() }
}

Or this:

val amplitudes = ThreadLocalRandom.current().let { rnd ->
    (0..5).map { rnd.nextInt() }.toIntArray()
}

Answer 4

Since Kotlin 1.3 was released there is no need to use Java'sjava.util.Random which would restrict your code to the JVM. Instead kotlin.random.Random was introduced which is available on all platforms that support Kotlin.

var amplititudes  = IntArray(10) { Random.nextInt() }.asList()

Since you work with a companion object, you don't need to worry about instanting a Random object each iteration (like it was with the Java one that you would have had to put in a variable).

Answer 5

To generate a random number of specified length of List and between certain limits, use:

val rnds = (1..10).map { (0..130).random() }

Where (1..0) -> return list of 10 items (0..130) -> return random number between given range

Answer 6

At this time, is not specified in your question the range of the Ints and how many do you need.

So I restrict the case to [n,m] interval, and I suppose you want all the m-n+1 elements.

Taking advantage of method shuffle of ArrayList,

var shuffledList = ArrayList((n..m).toList())
shuffledList.shuffle()