[KTLN-480] Convert a Collection Into an ArrayList in Kotlin (#813)

* added unit test code

* refactored code

* refactored code

* Extra Spacing Cleanup

---------

Co-authored-by: Brandon Ward <[email protected]>

Author: albertache1998

core-kotlin-modules/core-kotlin-collections-6/pom.xml

@@ -0,0 +1,16 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+    <artifactId>core-kotlin-collections-6</artifactId>
+    <name>core-kotlin-collections-6</name>
+    <packaging>jar</packaging>
+
+    <parent>
+        <groupId>com.baeldung</groupId>
+        <artifactId>core-kotlin-modules</artifactId>
+        <version>1.0.0-SNAPSHOT</version>
+    </parent>
+
+</project>

core-kotlin-modules/core-kotlin-collections-6/src/test/kotlin/com/baeldung/collectionToArrayList/CollectionToArrayListUnitTest.kt

@@ -0,0 +1,53 @@
+package com.baeldung.collectionToArrayList
+
+import org.junit.jupiter.api.Assertions.assertEquals
+import org.junit.jupiter.api.Test
+import kotlin.collections.ArrayList
+
+class CollectionToArrayListUnitTest {
+
+    @Test
+    fun `converts a Collection to ArrayList using the for loop and add method`() {
+        val collection: Collection<String> = listOf("Kotlin", "Java", "Scala")
+        val arrayList = ArrayList<String>()
+        for (element in collection) {
+            arrayList.add(element)
+        }
+
+        assertEquals(arrayListOf("Kotlin", "Java", "Scala"), arrayList)
+    }
+
+    @Test
+    fun `converts a Collection to ArrayList using the ArrayList constructor`() {
+        val collection: Collection<String> = listOf("Kotlin", "Java", "Scala")
+        val arrayList = ArrayList(collection)
+
+        assertEquals(arrayListOf("Kotlin", "Java", "Scala"), arrayList)
+    }
+
+    @Test
+    fun `converts a Collection to ArrayList using the toCollection method`() {
+        val collection: Collection<String> = listOf("Kotlin", "Java", "Scala")
+        val arrayList = collection.toCollection(ArrayList())
+
+        assertEquals(arrayListOf("Kotlin", "Java", "Scala"), arrayList)
+    }
+
+    @Test
+    fun `converts a Collection to ArrayList using the addAll method`() {
+        val collection: Collection<String> = listOf("Kotlin", "Java", "Scala")
+        val arrayList = ArrayList<String>()
+        arrayList.addAll(collection)
+
+        assertEquals(arrayListOf("Kotlin", "Java", "Scala"), arrayList)
+    }
+
+    @Test
+    fun `converts a Collection to ArrayList using the mapTo method`() {
+        val collection: Collection<String> = listOf("Kotlin", "Java", "Scala")
+        val arrayList = ArrayList<String>()
+        collection.mapTo(arrayList) { it }
+
+        assertEquals(arrayListOf("Kotlin", "Java", "Scala"), arrayList)
+    }
+}

core-kotlin-modules/pom.xml

@@ -36,6 +36,7 @@
         <module>core-kotlin-collections-3</module>
         <module>core-kotlin-collections-4</module>
         <module>core-kotlin-collections-5</module>
+        <module>core-kotlin-collections-6</module>
         <module>core-kotlin-collections-list</module>
         <module>core-kotlin-collections-list-2</module>
         <module>core-kotlin-collections-map</module>