Concatenate two arrays in Kotlin

This article explores different ways to concatenate two arrays in Kotlin. The requirement is to generate a new array that contains all elements of the first array, followed by all elements of the second array.

1. Using Plus Operator

A simple and fairly efficient solution to combine two arrays in Kotlin is with the plus operator. This is demonstrated below:

fun concatenate(a: IntArray, b: IntArray): IntArray {

return a + b

}

fun main() {

val A = intArrayOf(1, 2, 3)

val B = intArrayOf(4, 5)

val concat = concatenate(A, B)

println(concat.contentToString()) // [1, 2, 3, 4, 5]

}

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An equivalent way is to use the plus() function.

fun concatenate(a: IntArray, b: IntArray): IntArray {

return a.plus(b)

}

fun main() {

val A = intArrayOf(1, 2, 3)

val B = intArrayOf(4, 5)

val concat = concatenate(A, B)

println(concat.contentToString()) // [1, 2, 3, 4, 5]

}

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2. Using Spread Operator

This can also be done using the Spread operator (prefix the array with *). You can pass the contents of both arrays to the Array constructor using the Spread operator.

fun main() {

val A = intArrayOf(1, 2, 3)

val B = intArrayOf(4, 5)

val concat = intArrayOf(*A, *B)

println(concat.contentToString()) // [1, 2, 3, 4, 5]

}

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3. Using `System.arraycopy()` function

The System class’s arraycopy() function provides a convenient and efficient way to copy elements of an array into another array.

fun concatenate(a: IntArray, b: IntArray): IntArray {

val c = IntArray(a.size + b.size)

System.arraycopy(a, 0, c, 0, a.size)

System.arraycopy(b, 0, c, a.size, b.size)

return c

}

fun main() {

val A = intArrayOf(1, 2, 3)

val B = intArrayOf(4, 5)

val concat = concatenate(A, B)

println(concat.contentToString()) // [1, 2, 3, 4, 5]

}

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4. Using `copyOf()` function

You can also use the copyOf() function to copy elements of the first array, followed by the System.arraycopy() function to copy elements of the second array, as shown below:

fun concatenate(a: IntArray, b: IntArray): IntArray {

val result = a.copyOf(a.size + b.size)

System.arraycopy(b, 0, result, a.size, b.size)

return result

}

fun main() {

val A = intArrayOf(1, 2, 3)

val B = intArrayOf(4, 5)

val concat = concatenate(A, B)

println(concat.contentToString()) // [1, 2, 3, 4, 5]

}

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That’s all about concatenating two arrays in Kotlin.

Concatenate two arrays in Kotlin

1. Using Plus Operator

2. Using Spread Operator

3. Using System.arraycopy() function

4. Using copyOf() function

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3. Using `System.arraycopy()` function

4. Using `copyOf()` function