list and set difference (#12787)

* BAEL-5751 test commit for checkin builds

* BAEL-5751 compiled with java 8

* BAEL-5751 small update

* BAEL-5751 added the core code

* BAEL-5751 moved code to a different module

core-java-modules/core-java-collections-4/src/test/java/com/baeldung/listandset/ListAndSetUnitTest.java

@@ -0,0 +1,51 @@
+package com.baeldung.listandset;
+
+import org.junit.Test;
+import java.util.*;
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertTrue;
+
+public class ListAndSetUnitTest {
+
+    @Test
+    public void givenList_whenDuplicates_thenAllowed(){
+        List<Integer> integerList = new ArrayList<>();
+        integerList.add(2);
+        integerList.add(3);
+        integerList.add(4);
+        integerList.add(4);
+        assertEquals(integerList.size(), 4);
+    }
+
+    @Test
+    public void givenSet_whenDuplicates_thenNotAllowed(){
+        Set<Integer> integerSet = new HashSet<>();
+        integerSet.add(2);
+        integerSet.add(3);
+        integerSet.add(4);
+        integerSet.add(4);
+        assertEquals(integerSet.size(), 3);
+    }
+
+    @Test
+    public void givenSet_whenOrdering_thenMayBeAllowed(){
+        Set<Integer> set1 = new LinkedHashSet<>();
+        set1.add(2);
+        set1.add(3);
+        set1.add(4);
+        Set<Integer> set2 = new LinkedHashSet<>();
+        set2.add(2);
+        set2.add(3);
+        set2.add(4);
+        boolean ordered = true;
+        Object[] arr1 = set1.toArray();
+        Object[] arr2 = set2.toArray();
+        for(int i=0; i < arr1.length; i++){
+            if (!arr1[i].equals(arr2[i])) {
+                ordered = false;
+                break;
+            }
+        }
+        assertTrue(ordered);
+    }
+}