Merge pull request #5559 from laurentiud/master

BAEL-2218 Example of sorting in Kotlin

core-kotlin/src/main/kotlin/com/baeldung/sorting/SortingExample.kt

@@ -0,0 +1,44 @@
+package com.baeldung.sorting
+
+import kotlin.comparisons.*
+
+fun sortMethodUsage() {
+    val sortedValues = mutableListOf(1, 2, 7, 6, 5, 6)
+    sortedValues.sort()
+    println(sortedValues)
+}
+
+fun sortByMethodUsage() {
+    val sortedValues = mutableListOf(1 to "a", 2 to "b", 7 to "c", 6 to "d", 5 to "c", 6 to "e")
+    sortedValues.sortBy { it.second }
+    println(sortedValues)
+}
+
+fun sortWithMethodUsage() {
+    val sortedValues = mutableListOf(1 to "a", 2 to "b", 7 to "c", 6 to "d", 5 to "c", 6 to "e")
+    sortedValues.sortWith(compareBy({it.second}, {it.first}))
+    println(sortedValues)
+}
+
+fun <T : kotlin.Comparable<T>> getSimpleComparator() : Comparator<T> {
+    val ascComparator = naturalOrder<T>()
+    return ascComparator
+}
+
+fun getComplexComparator() {
+    val complexComparator = compareBy<Pair<Int, String>>({it.first}, {it.second})
+}
+
+fun nullHandlingUsage() {
+    val sortedValues = mutableListOf(1 to "a", 2 to null, 7 to "c", 6 to "d", 5 to "c", 6 to "e")
+    sortedValues.sortWith(nullsLast(compareBy { it.second }))
+    println(sortedValues)
+}
+
+fun extendedComparatorUsage() {
+    val students = mutableListOf(21 to "Helen", 21 to "Tom", 20 to "Jim")
+
+    val ageComparator = compareBy<Pair<Int, String?>> {it.first}
+    val ageAndNameComparator = ageComparator.thenByDescending {it.second}
+    println(students.sortedWith(ageAndNameComparator))
+}

core-kotlin/src/test/kotlin/com/baeldung/sorting/SortingExampleKtTest.kt

@@ -0,0 +1,14 @@
+package com.baeldung.sorting
+
+import org.junit.jupiter.api.Test
+
+import org.junit.jupiter.api.Assertions.*
+
+class SortingExampleKtTest {
+
+    @Test
+    fun naturalOrderComparator_ShouldBeAscendingTest() {
+        val resultingList = listOf(1, 5, 6, 6, 2, 3, 4).sortedWith(getSimpleComparator())
+        assertTrue(listOf(1, 2, 3, 4, 5, 6, 6) == resultingList)
+    }
+}