BAEL-4944: Update code samples for the Removing all duplicates from a List in Java (#10717)

Co-authored-by: Krzysztof Woyke <krzysztof.woyke.sp@lhsystems.com>

core-java-modules/core-java-collections-list/src/test/java/com/baeldung/collections/JavaCollectionCleanupUnitTest.java

@@ -1,11 +1,14 @@
 package com.baeldung.collections;
 
+import static org.hamcrest.Matchers.containsInAnyOrder;
+import static org.hamcrest.Matchers.containsInRelativeOrder;
 import static org.hamcrest.Matchers.hasSize;
 import static org.junit.Assert.assertThat;
 
 import java.util.ArrayList;
 import java.util.Collections;
 import java.util.HashSet;
+import java.util.LinkedHashSet;
 import java.util.List;
 
 import org.apache.commons.collections4.CollectionUtils;
@@ -22,7 +25,7 @@ public class JavaCollectionCleanupUnitTest {
     // tests - removing nulls
 
     @Test
-    public final void givenListContainsNulls_whenRemovingNullsWithPlainJava_thenCorrect() {
+    public void givenListContainsNulls_whenRemovingNullsWithPlainJava_thenCorrect() {
         final List<Integer> list = Lists.newArrayList(null, 1, null);
         while (list.remove(null))
             ;
@@ -31,7 +34,7 @@ public class JavaCollectionCleanupUnitTest {
     }
 
     @Test
-    public final void givenListContainsNulls_whenRemovingNullsWithPlainJavaAlternative_thenCorrect() {
+    public void givenListContainsNulls_whenRemovingNullsWithPlainJavaAlternative_thenCorrect() {
         final List<Integer> list = Lists.newArrayList(null, 1, null);
         list.removeAll(Collections.singleton(null));
 
@@ -39,7 +42,7 @@ public class JavaCollectionCleanupUnitTest {
     }
 
     @Test
-    public final void givenListContainsNulls_whenRemovingNullsWithGuavaV1_thenCorrect() {
+    public void givenListContainsNulls_whenRemovingNullsWithGuavaV1_thenCorrect() {
         final List<Integer> list = Lists.newArrayList(null, 1, null);
         Iterables.removeIf(list, Predicates.isNull());
 
@@ -47,7 +50,7 @@ public class JavaCollectionCleanupUnitTest {
     }
 
     @Test
-    public final void givenListContainsNulls_whenRemovingNullsWithGuavaV2_thenCorrect() {
+    public void givenListContainsNulls_whenRemovingNullsWithGuavaV2_thenCorrect() {
         final List<Integer> list = Lists.newArrayList(null, 1, null, 2, 3);
         final List<Integer> listWithoutNulls = Lists.newArrayList(Iterables.filter(list, Predicates.notNull()));
 
@@ -55,7 +58,7 @@ public class JavaCollectionCleanupUnitTest {
     }
 
     @Test
-    public final void givenListContainsNulls_whenRemovingNullsWithCommonsCollections_thenCorrect() {
+    public void givenListContainsNulls_whenRemovingNullsWithCommonsCollections_thenCorrect() {
         final List<Integer> list = Lists.newArrayList(null, 1, 2, null, 3, null);
         CollectionUtils.filter(list, PredicateUtils.notNullPredicate());
 
@@ -65,19 +68,38 @@ public class JavaCollectionCleanupUnitTest {
     // tests - remove duplicates
 
     @Test
-    public final void givenListContainsDuplicates_whenRemovingDuplicatesWithPlainJava_thenCorrect() {
-        final List<Integer> listWithDuplicates = Lists.newArrayList(0, 1, 2, 3, 0, 0);
+    public void givenListContainsDuplicates_whenRemovingDuplicatesWithPlainJava_thenCorrect() {
+        final List<Integer> listWithDuplicates = Lists.newArrayList(5, 0, 3, 1, 2, 3, 0, 0);
         final List<Integer> listWithoutDuplicates = new ArrayList<>(new HashSet<>(listWithDuplicates));
 
-        assertThat(listWithoutDuplicates, hasSize(4));
+        assertThat(listWithoutDuplicates, hasSize(5));
+        assertThat(listWithoutDuplicates, containsInAnyOrder(5, 0, 3, 1, 2));
     }
 
     @Test
-    public final void givenListContainsDuplicates_whenRemovingDuplicatesWithGuava_thenCorrect() {
-        final List<Integer> listWithDuplicates = Lists.newArrayList(0, 1, 2, 3, 0, 0);
-        final List<Integer> listWithoutDuplicates = Lists.newArrayList(Sets.newHashSet(listWithDuplicates));
+    public void givenListContainsDuplicates_whenRemovingDuplicatesPreservingOrderWithPlainJava_thenCorrect() {
+        final List<Integer> listWithDuplicates = Lists.newArrayList(5, 0, 3, 1, 2, 3, 0, 0);
+        final List<Integer> listWithoutDuplicates = new ArrayList<>(new LinkedHashSet<>(listWithDuplicates));
 
-        assertThat(listWithoutDuplicates, hasSize(4));
+        assertThat(listWithoutDuplicates, hasSize(5));
+        assertThat(listWithoutDuplicates, containsInRelativeOrder(5, 0, 3, 1, 2));
     }
 
+    @Test
+    public void givenListContainsDuplicates_whenRemovingDuplicatesWithGuava_thenCorrect() {
+        final List<Integer> listWithDuplicates = Lists.newArrayList(5, 0, 3, 1, 2, 3, 0, 0);
+        final List<Integer> listWithoutDuplicates = Lists.newArrayList(Sets.newHashSet(listWithDuplicates));
+
+        assertThat(listWithoutDuplicates, hasSize(5));
+        assertThat(listWithoutDuplicates, containsInAnyOrder(5, 0, 3, 1, 2));
+    }
+
+    @Test
+    public void givenListContainsDuplicates_whenRemovingDuplicatesPreservingOrderWithGuava_thenCorrect() {
+        final List<Integer> listWithDuplicates = Lists.newArrayList(5, 0, 3, 1, 2, 3, 0, 0);
+        final List<Integer> listWithoutDuplicates = Lists.newArrayList(Sets.newLinkedHashSet(listWithDuplicates));
+
+        assertThat(listWithoutDuplicates, hasSize(5));
+        assertThat(listWithoutDuplicates, containsInRelativeOrder(5, 0, 3, 1, 2));
+    }
 }

core-java-modules/core-java-collections-list/src/test/java/com/baeldung/java8/Java8CollectionCleanupUnitTest.java

@@ -7,6 +7,7 @@ import java.util.List;
 import java.util.Objects;
 import java.util.stream.Collectors;
 
+import static org.hamcrest.Matchers.containsInAnyOrder;
 import static org.hamcrest.Matchers.hasSize;
 import static org.junit.Assert.assertThat;
 
@@ -40,10 +41,11 @@ public class Java8CollectionCleanupUnitTest {
 
     @Test
     public void givenListContainsDuplicates_whenRemovingDuplicatesWithJava8_thenCorrect() {
-        final List<Integer> listWithDuplicates = Lists.newArrayList(1, 1, 2, 2, 3, 3);
-        final List<Integer> listWithoutDuplicates = listWithDuplicates.parallelStream().distinct().collect(Collectors.toList());
+        final List<Integer> listWithDuplicates = Lists.newArrayList(5, 0, 3, 1, 2, 3, 0, 0);
+        final List<Integer> listWithoutDuplicates = listWithDuplicates.stream().distinct().collect(Collectors.toList());
 
-        assertThat(listWithoutDuplicates, hasSize(3));
+        assertThat(listWithoutDuplicates, hasSize(5));
+        assertThat(listWithoutDuplicates, containsInAnyOrder(5, 0, 3, 1, 2));
     }
 
 }