Kotlin Program to Convert List (ArrayList) to Array and Vice-Versa

Converting between List (or ArrayList) and Array is a common task in Kotlin programming. Lists are ordered collections that can contain duplicate elements and can dynamically grow, while arrays have a fixed size but provide fast access to elements. This article will demonstrate three different Kotlin Program to Convert List (ArrayList) to Array and Vice-Versa , including explanations, code implementations, and outputs for each example.

1. Converting List (ArrayList) to Array

1.1 Example 1: Using toTypedArray

Program Explanation

The toTypedArray function converts a List to an Array of the same type. This method is straightforward and commonly used for conversion.

Code Implementation

fun main() {
    val list = listOf("Kotlin", "Java", "Python")

    // Convert list to array
    val array: Array<String> = list.toTypedArray()

    println("Original List: $list")
    println("Converted Array: ${array.joinToString()}")
}

Output

Original List: [Kotlin, Java, Python]
Converted Array: Kotlin, Java, Python

1.2 Example 2: Using ArrayList and toArray

Program Explanation

The toArray method is used to convert an ArrayList to an array. This method is useful when working with Java interoperability.

Code Implementation

fun main() {
    val arrayList = arrayListOf(1, 2, 3, 4, 5)

    // Convert ArrayList to array
    val array = arrayList.toArray(arrayOfNulls<Int>(arrayList.size))

    println("Original ArrayList: $arrayList")
    println("Converted Array: ${array.joinToString()}")
}

Output

Original ArrayList: [1, 2, 3, 4, 5]
Converted Array: 1, 2, 3, 4, 5

1.3 Example 3: Using map and toTypedArray

Program Explanation

This example demonstrates how to use the map function to transform elements before converting the list to an array using toTypedArray.

Code Implementation

fun main() {
    val list = listOf(1, 2, 3, 4, 5)

    // Convert list to array with transformation
    val array: Array<String> = list.map { it.toString() }.toTypedArray()

    println("Original List: $list")
    println("Converted Array: ${array.joinToString()}")
}

Output

Original List: [1, 2, 3, 4, 5]
Converted Array: 1, 2, 3, 4, 5

2. Converting Array to List (ArrayList)

2.1 Example 1: Using toList

Program Explanation

The toList function converts an Array to an immutable List. This is a simple and direct method to perform the conversion.

Code Implementation

fun main() {
    val array = arrayOf("Kotlin", "Java", "Python")

    // Convert array to list
    val list: List<String> = array.toList()

    println("Original Array: ${array.joinToString()}")
    println("Converted List: $list")
}

Output

Original Array: Kotlin, Java, Python
Converted List: [Kotlin, Java, Python]

2.2 Example 2: Using ArrayList Constructor

Program Explanation

This method uses the ArrayList constructor to convert an Array to a mutable ArrayList. This is useful when you need a mutable list.

Code Implementation

fun main() {
    val array = arrayOf(1, 2, 3, 4, 5)

    // Convert array to ArrayList
    val arrayList = ArrayList(array.asList())

    println("Original Array: ${array.joinToString()}")
    println("Converted ArrayList: $arrayList")
}

Output

Original Array: 1, 2, 3, 4, 5
Converted ArrayList: [1, 2, 3, 4, 5]

2.3 Example 3: Using forEach

Program Explanation

In this example, we iterate through the Array and add each element to an ArrayList. This approach allows for more complex operations during the conversion process.

Code Implementation

fun main() {
    val array = arrayOf(1, 2, 3, 4, 5)

    // Convert array to ArrayList with iteration
    val arrayList = ArrayList<Int>()
    array.forEach { arrayList.add(it) }

    println("Original Array: ${array.joinToString()}")
    println("Converted ArrayList: $arrayList")
}

Output

Original Array: 1, 2, 3, 4, 5
Converted ArrayList: [1, 2, 3, 4, 5]

Conclusion

In this article, we explored six different methods for converting between List (ArrayList) and Array in Kotlin. The first set of examples showed how to convert lists to arrays using toTypedArray, toArray, and map functions. The second set of examples demonstrated converting arrays to lists using toList, ArrayList constructor, and forEach loop. Each method offers a different approach, allowing you to choose the one that best suits your specific requirements. By understanding these techniques, you can effectively manage and manipulate collections in your Kotlin programs.