A Guide to LinkedHashSet in Java (#12932)

* Creating a Deep vs Shallow Copy of an Object in Java

* completed tests for LinkedHashSet

* update

* updated PR

core-java-modules/core-java-collections-set-2/src/test/java/com/baeldung/linkedhashset/LinkedHashSetUnitTest.java

@@ -0,0 +1,141 @@
+package com.baeldung.linkedhashset;
+
+import org.junit.jupiter.api.Test;
+
+import java.util.*;
+import java.util.concurrent.atomic.AtomicInteger;
+
+import static org.junit.Assert.*;
+
+
+public class LinkedHashSetUnitTest{
+
+
+    @Test
+    void whenCreatingLinkedHashSet_shouldBeEmpty(){
+        Set<String> linkedHashSet = new LinkedHashSet<>();
+        assertTrue(linkedHashSet.isEmpty());
+    }
+
+    @Test
+    void whenCreatingLinkedHashSetWithInitialCapacity_shouldBeEmpty(){
+        LinkedHashSet<String> linkedHashSet = new LinkedHashSet<>(20);
+        assertTrue(linkedHashSet.isEmpty());
+    }
+
+    @Test
+    void whenCreatingLinkedHashSetWithExistingCollection_shouldContainAllElementOfCollection(){
+        Collection<String> data = Arrays.asList("first", "second", "third", "fourth", "fifth");
+        LinkedHashSet<String> linkedHashSet = new LinkedHashSet<>(data);
+
+        assertFalse(linkedHashSet.isEmpty());
+        assertEquals(linkedHashSet.size(), data.size());
+        assertTrue(linkedHashSet.containsAll(data) && data.containsAll(linkedHashSet));
+    }
+
+    @Test
+    void whenCreatingLinkedHashSetWithInitialCapacityAndLoadFactor_shouldBeEmpty(){
+        LinkedHashSet<String> linkedHashSet = new LinkedHashSet<>(20, 3);
+        assertTrue(linkedHashSet.isEmpty());
+    }
+
+    @Test
+    void whenAddingElement_shouldAddElement(){
+        Set<Integer> linkedHashSet = new LinkedHashSet<>();
+        assertTrue(linkedHashSet.add(0));
+        assertFalse(linkedHashSet.add(0));
+        assertTrue(linkedHashSet.contains(0));
+
+    }
+
+    @Test
+    void whenAddingCollection_shouldAddAllContentOfCollection(){
+        Collection<Integer> data = Arrays.asList(1,2,3);
+        LinkedHashSet<Integer> linkedHashSet = new LinkedHashSet<>();
+
+        assertTrue(linkedHashSet.addAll(data));
+        assertTrue(data.containsAll(linkedHashSet) && linkedHashSet.containsAll(data));
+    }
+
+    @Test
+    void whenAddingCollectionWithDuplicateElements_shouldMaintainUniqueValuesInSet(){
+        LinkedHashSet<Integer> linkedHashSet = new LinkedHashSet<>();
+        linkedHashSet.add(2);
+        Collection<Integer> data = Arrays.asList(1, 1, 2, 3);
+
+        assertTrue(linkedHashSet.addAll(data));
+        assertEquals(linkedHashSet.size(), 3);
+        assertTrue(data.containsAll(linkedHashSet) && linkedHashSet.containsAll(data));
+    }
+
+    @Test
+    void whenIteratingWithIterator_assertThatElementIsPresent(){
+        LinkedHashSet<Integer> linkedHashSet = new LinkedHashSet<>();
+        linkedHashSet.add(0);
+        linkedHashSet.add(1);
+        linkedHashSet.add(2);
+
+        Iterator<Integer> iterator = linkedHashSet.iterator();
+        for (int i = 0; i < linkedHashSet.size(); i++) {
+            int nextData = iterator.next();
+            assertEquals(nextData, i);
+        }
+    }
+
+    @Test
+    void whenIteratingWithSpliterator_assertThatElementIsPresent(){
+        LinkedHashSet<Integer> linkedHashSet = new LinkedHashSet<>();
+        linkedHashSet.add(0);
+        linkedHashSet.add(1);
+        linkedHashSet.add(2);
+
+        Spliterator<Integer> spliterator = linkedHashSet.spliterator();
+        AtomicInteger counter = new AtomicInteger();
+        spliterator.forEachRemaining(data -> {
+            assertEquals((int)data,  counter.get());
+            counter.getAndIncrement();
+        });
+    }
+
+    @Test
+    void whenRemovingAnElement_shouldRemoveElement(){
+        Collection<String> data = Arrays.asList("first", "second", "third", "fourth", "fifth");
+        LinkedHashSet<String> linkedHashSet = new LinkedHashSet<>(data);
+
+        assertTrue(linkedHashSet.remove("second"));
+        assertFalse(linkedHashSet.contains("second"));
+    }
+
+    @Test
+    void whenRemovingAnElementGreaterThanTwo_shouldRemoveElement(){
+        LinkedHashSet<Integer> linkedHashSet = new LinkedHashSet<>();
+        linkedHashSet.add(0);
+        linkedHashSet.add(1);
+        linkedHashSet.add(2);
+        linkedHashSet.add(3);
+        linkedHashSet.add(4);
+
+        linkedHashSet.removeIf(data -> data > 2);
+        assertFalse(linkedHashSet.contains(3));
+        assertFalse(linkedHashSet.contains(4));
+    }
+
+    @Test
+    void whenRemovingAnElementWithIterator_shouldRemoveElement(){
+        LinkedHashSet<Integer> linkedHashSet = new LinkedHashSet<>();
+        linkedHashSet.add(0);
+        linkedHashSet.add(1);
+        linkedHashSet.add(2);
+
+        Iterator<Integer> iterator = linkedHashSet.iterator();
+        int elementToRemove = 1;
+        assertTrue(linkedHashSet.contains(elementToRemove));
+        while(iterator.hasNext()){
+            if(elementToRemove == iterator.next()){
+                iterator.remove();
+            }
+        }
+        assertFalse(linkedHashSet.contains(elementToRemove));
+    }
+
+}