Guide to HashSet (#3165)

core-java/src/test/java/com/baeldung/collection/WhenUsingHashSet.java

@@ -0,0 +1,93 @@
+package com.baeldung.collection;
+
+import java.util.ConcurrentModificationException;
+import java.util.HashSet;
+import java.util.Iterator;
+import java.util.Set;
+
+import org.junit.Assert;
+import org.junit.Test;
+
+public class WhenUsingHashSet {
+
+    @Test
+    public void whenAddingElement_shouldAddElement() {
+        Set<String> hashset = new HashSet<>();
+        Assert.assertTrue(hashset.add("String Added"));
+    }
+
+    @Test
+    public void whenCheckingForElement_shouldSearchForElement() {
+        Set<String> hashsetContains = new HashSet<>();
+        hashsetContains.add("String Added");
+        Assert.assertTrue(hashsetContains.contains("String Added"));
+    }
+
+    @Test
+    public void whenCheckingTheSizeOfHashSet_shouldReturnThesize() {
+        Set<String> hashSetSize = new HashSet<>();
+        hashSetSize.add("String Added");
+        Assert.assertEquals(1, hashSetSize.size());
+    }
+
+    @Test
+    public void whenCheckingForEmptyHashSet_shouldCheckForEmpty() {
+        Set<String> emptyHashSet = new HashSet<>();
+        Assert.assertTrue(emptyHashSet.isEmpty());
+    }
+
+    @Test
+    public void whenRemovingElement_shouldRemoveElement() {
+        Set<String> removeFromHashSet = new HashSet<>();
+        removeFromHashSet.add("String Added");
+        Assert.assertTrue(removeFromHashSet.remove("String Added"));
+    }
+
+    @Test
+    public void whenClearingHashSet_shouldClearHashSet() {
+        Set<String> clearHashSet = new HashSet<>();
+        clearHashSet.add("String Added");
+        clearHashSet.clear();
+        Assert.assertTrue(clearHashSet.isEmpty());
+    }
+
+    @Test
+    public void whenIteratingHashSet_shouldIterateHashSet() {
+        Set<String> hashset = new HashSet<>();
+        hashset.add("First");
+        hashset.add("Second");
+        hashset.add("Third");
+        Iterator<String> itr = hashset.iterator();
+        while (itr.hasNext()) {
+            System.out.println(itr.next());
+        }
+    }
+
+    @Test(expected = ConcurrentModificationException.class)
+    public void whenModifyingHashSetWhileIterating_shouldThrowException() {
+        Set<String> hashset = new HashSet<>();
+        hashset.add("First");
+        hashset.add("Second");
+        hashset.add("Third");
+        Iterator<String> itr = hashset.iterator();
+        while (itr.hasNext()) {
+            itr.next();
+            hashset.remove("Second");
+        }
+    }
+
+    @Test
+    public void whenRemovingElementUsingIterator_shouldRemoveElement() {
+        Set<String> hashset = new HashSet<>();
+        hashset.add("First");
+        hashset.add("Second");
+        hashset.add("Third");
+        Iterator<String> itr = hashset.iterator();
+        while (itr.hasNext()) {
+            String element = itr.next();
+            if (element.equals("Second"))
+                itr.remove();
+        }
+        Assert.assertEquals(2, hashset.size());
+    }
+}