This commit is related to the article BAEL-7172 (#15232)

This commit aims to add two classes that provide insights about the time complexity of Collections.sort().

core-java-modules/core-java-collections-5/src/main/java/com/baeldung/collectionssortcomplexity/CollectionsSortTimeComplexityJMH.java

@@ -0,0 +1,60 @@
+package com.baeldung.collectionssortcomplexity;
+
+import org.openjdk.jmh.annotations.*;
+
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
+import java.util.concurrent.TimeUnit;
+
+@BenchmarkMode(Mode.AverageTime)
+@OutputTimeUnit(TimeUnit.MILLISECONDS)
+@Fork(value = 1, warmups = 1)
+@Warmup(iterations = 5, time = 1)
+@Measurement(iterations = 5, time = 1)
+public class CollectionsSortTimeComplexityJMH {
+
+    public static void main(String[] args) throws Exception {
+        org.openjdk.jmh.Main.main(args);
+
+    }
+
+    @Benchmark
+    public void measureCollectionsSortBestCase(BestCaseBenchmarkState state) {
+        List<Integer> sortedList = new ArrayList<>(state.sortedList);
+        Collections.sort(sortedList);
+    }
+
+    @Benchmark
+    public void measureCollectionsSortAverageWorstCase(AverageWorstCaseBenchmarkState state) {
+        List<Integer> unsortedList = new ArrayList<>(state.unsortedList);
+        Collections.sort(unsortedList);
+    }
+
+    @State(Scope.Benchmark)
+    public static class BestCaseBenchmarkState {
+        List<Integer> sortedList;
+
+        @Setup(Level.Trial)
+        public void setUp() {
+            sortedList = new ArrayList<>();
+            for (int i = 1; i <= 1000000; i++) {
+                sortedList.add(i);
+            }
+        }
+    }
+
+    @State(Scope.Benchmark)
+    public static class AverageWorstCaseBenchmarkState {
+        List<Integer> unsortedList;
+
+        @Setup(Level.Trial)
+        public void setUp() {
+            unsortedList = new ArrayList<>();
+            for (int i = 1000000; i > 0; i--) {
+                unsortedList.add(i);
+            }
+        }
+    }
+
+}

core-java-modules/core-java-collections-5/src/main/java/com/baeldung/collectionssortcomplexity/CollectionsSortTimeComplexityMain.java

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+package com.baeldung.collectionssortcomplexity;
+
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.List;
+
+public class CollectionsSortTimeComplexityMain {
+    // O(n log n) Time Complexity Example
+    public static void worstAndAverageCasesTimeComplexity() {
+        Integer[] sortedArray = {20, 21, 22, 23, 24, 25, 26, 17, 28, 29, 30, 31, 18, 19, 32, 33, 34, 27, 35};
+        List<Integer> list = Arrays.asList(sortedArray);
+        Collections.shuffle(list);
+        long startTime = System.nanoTime();
+        Collections.sort(list);
+        long endTime = System.nanoTime();
+        System.out.println("Execution Time for O(n log n): " + (endTime - startTime) + " nanoseconds");
+    }
+
+    // O(n) Time Complexity Example
+    public static void bestCaseTimeComplexity() {
+        Integer[] sortedArray = {19, 22, 19, 22, 24, 25, 17, 11, 22, 23, 28, 23, 0, 1, 12, 9, 13, 27, 15};
+        List<Integer> list = Arrays.asList(sortedArray);
+        long startTime = System.nanoTime();
+        Collections.sort(list);
+        long endTime = System.nanoTime();
+        System.out.println("Execution Time for O(n): " + (endTime - startTime) + " nanoseconds");
+    }
+
+    public static void main(String[] args) {
+        worstAndAverageCasesTimeComplexity();
+        bestCaseTimeComplexity();
+    }
+}