HashSet and TreeSet comparison (eugenp#1698)

core-java/src/test/java/com/baeldung/java/set/SetTest.java

@@ -0,0 +1,89 @@
+package com.baeldung.java.set;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertTrue;
+
+import java.util.ConcurrentModificationException;
+import java.util.HashSet;
+import java.util.Iterator;
+import java.util.Set;
+import java.util.TreeSet;
+
+import org.junit.Test;
+
+public class SetTest {
+
+    @Test
+    public void givenTreeSet_whenRetrievesObjects_thenNaturalOrder() {
+        Set<String> set = new TreeSet<>();
+        set.add("Baeldung");
+        set.add("is");
+        set.add("Awesome");
+        assertEquals(3, set.size());
+        assertTrue(set.iterator()
+            .next()
+            .equals("Awesome"));
+    }
+
+    @Test(expected = NullPointerException.class)
+    public void givenTreeSet_whenAddNullObject_thenNullPointer() {
+        Set<String> set = new TreeSet<>();
+        set.add("Baeldung");
+        set.add("is");
+        set.add(null);
+    }
+
+    @Test
+    public void givenHashSet_whenAddNullObject_thenOK() {
+        Set<String> set = new HashSet<>();
+        set.add("Baeldung");
+        set.add("is");
+        set.add(null);
+        assertEquals(3, set.size());
+    }
+
+    @Test
+    public void givenHashSetAndTreeSet_whenAddObjects_thenHashSetIsFaster() {
+        Set<String> set = new HashSet<>();
+        long startTime = System.nanoTime();
+        set.add("Baeldung");
+        set.add("is");
+        set.add("Awesome");
+        long endTime = System.nanoTime();
+        long duration1 = (endTime - startTime);
+
+        Set<String> set2 = new TreeSet<>();
+        startTime = System.nanoTime();
+        set2.add("Baeldung");
+        set2.add("is");
+        set2.add("Awesome");
+        endTime = System.nanoTime();
+        long duration2 = (endTime - startTime);
+        assertTrue(duration1 < duration2);
+    }
+
+    @Test
+    public void givenHashSetAndTreeSet_whenAddDuplicates_thenOnlyUnique() {
+        Set<String> set = new HashSet<>();
+        set.add("Baeldung");
+        set.add("Baeldung");
+        assertTrue(set.size() == 1);
+
+        Set<String> set2 = new TreeSet<>();
+        set2.add("Baeldung");
+        set2.add("Baeldung");
+        assertTrue(set2.size() == 1);
+    }
+
+    @Test(expected = ConcurrentModificationException.class)
+    public void givenHashSet_whenModifyWhenIterator_thenFailFast() {
+        Set<String> set = new HashSet<>();
+        set.add("Baeldung");
+        Iterator<String> it = set.iterator();
+
+        while (it.hasNext()) {
+            set.add("Awesome");
+            it.next();
+        }
+    }
+}