Enhance docs, add tests in GenericArrayListQueue (#6016)

Author: Hardvan

src/main/java/com/thealgorithms/datastructures/queues/GenericArrayListQueue.java

@@ -4,43 +4,46 @@
 import java.util.List;
 
 /**
- * This class implements a GenericArrayListQueue.
+ * This class implements a GenericArrayListQueue, a queue data structure that
+ * holds elements of any type specified at runtime, allowing flexibility in the type
+ * of elements it stores.
  *
- * A GenericArrayListQueue data structure functions the same as any
- * specific-typed queue. The GenericArrayListQueue holds elements of types
- * to-be-specified at runtime. The elements that are added first are the first
- * to be removed (FIFO). New elements are added to the back/rear of the queue.
+ * <p>The GenericArrayListQueue operates on a First-In-First-Out (FIFO) basis, where
+ * elements added first are the first to be removed. New elements are added to the back
+ * (or rear) of the queue, while removal of elements occurs from the front.
+ *
+ * @param <T> The type of elements held in this queue.
  */
 public class GenericArrayListQueue<T> {
 
     /**
-     * The generic List for the queue. T is the generic element type.
+     * A list that stores the queue's elements in insertion order.
      */
     private final List<T> elementList = new ArrayList<>();
 
     /**
      * Checks if the queue is empty.
      *
-     * @return True if the queue is empty, false otherwise.
+     * @return {@code true} if the queue has no elements; {@code false} otherwise.
      */
-    private boolean isEmpty() {
+    public boolean isEmpty() {
         return elementList.isEmpty();
     }
 
     /**
-     * Returns the element at the front of the queue without removing it.
+     * Retrieves, but does not remove, the element at the front of the queue.
      *
-     * @return The element at the front of the queue, or null if the queue is empty.
+     * @return The element at the front of the queue, or {@code null} if the queue is empty.
      */
     public T peek() {
         return isEmpty() ? null : elementList.getFirst();
     }
 
     /**
-     * Inserts an element of type T to the back of the queue.
+     * Inserts an element at the back of the queue.
      *
-     * @param element the element to be added to the queue.
-     * @return True if the element was added successfully.
+     * @param element The element to be added to the queue.
+     * @return {@code true} if the element was successfully added.
      */
     public boolean add(T element) {
         return elementList.add(element);
@@ -49,7 +52,7 @@ public boolean add(T element) {
     /**
      * Retrieves and removes the element at the front of the queue.
      *
-     * @return The element removed from the front of the queue, or null if the queue is empty.
+     * @return The element removed from the front of the queue, or {@code null} if the queue is empty.
      */
     public T poll() {
         return isEmpty() ? null : elementList.removeFirst();

src/test/java/com/thealgorithms/datastructures/queues/GenericArrayListQueueTest.java

@@ -1,6 +1,7 @@
 package com.thealgorithms.datastructures.queues;
 
 import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
 import static org.junit.jupiter.api.Assertions.assertNull;
 import static org.junit.jupiter.api.Assertions.assertTrue;
 
@@ -13,43 +14,87 @@ void testAdd() {
         GenericArrayListQueue<Integer> queue = new GenericArrayListQueue<>();
         assertTrue(queue.add(10));
         assertTrue(queue.add(20));
+        assertEquals(10, queue.peek()); // Ensure the first added element is at the front
     }
 
     @Test
     void testPeek() {
         GenericArrayListQueue<Integer> queue = new GenericArrayListQueue<>();
-        assertNull(queue.peek());
+        assertNull(queue.peek(), "Peek should return null for an empty queue");
 
         queue.add(10);
         queue.add(20);
 
-        assertEquals(10, queue.peek());
+        assertEquals(10, queue.peek(), "Peek should return the first element (10)");
         queue.poll();
-        assertEquals(20, queue.peek());
+        assertEquals(20, queue.peek(), "Peek should return the next element (20) after poll");
     }
 
     @Test
     void testPoll() {
         GenericArrayListQueue<Integer> queue = new GenericArrayListQueue<>();
-        assertNull(queue.poll());
+        assertNull(queue.poll(), "Poll should return null for an empty queue");
 
         queue.add(10);
         queue.add(20);
 
-        assertEquals(10, queue.poll());
-        assertEquals(20, queue.poll());
-        assertNull(queue.poll());
+        assertEquals(10, queue.poll(), "Poll should return and remove the first element (10)");
+        assertEquals(20, queue.poll(), "Poll should return and remove the next element (20)");
+        assertNull(queue.poll(), "Poll should return null when queue is empty after removals");
     }
 
     @Test
     void testIsEmpty() {
         GenericArrayListQueue<Integer> queue = new GenericArrayListQueue<>();
-        assertNull(queue.peek());
-        assertNull(queue.poll());
+        assertTrue(queue.isEmpty(), "Queue should initially be empty");
 
         queue.add(30);
-        assertEquals(30, queue.peek());
-        assertEquals(30, queue.poll());
-        assertNull(queue.peek());
+        assertFalse(queue.isEmpty(), "Queue should not be empty after adding an element");
+        queue.poll();
+        assertTrue(queue.isEmpty(), "Queue should be empty after removing the only element");
+    }
+
+    @Test
+    void testClearQueueAndReuse() {
+        GenericArrayListQueue<Integer> queue = new GenericArrayListQueue<>();
+        queue.add(5);
+        queue.add(10);
+        queue.poll();
+        queue.poll(); // Remove all elements
+
+        assertTrue(queue.isEmpty(), "Queue should be empty after all elements are removed");
+        assertNull(queue.peek(), "Peek should return null on an empty queue after clear");
+        assertTrue(queue.add(15), "Queue should be reusable after being emptied");
+        assertEquals(15, queue.peek(), "Newly added element should be accessible in the empty queue");
+    }
+
+    @Test
+    void testOrderMaintained() {
+        GenericArrayListQueue<String> queue = new GenericArrayListQueue<>();
+        queue.add("First");
+        queue.add("Second");
+        queue.add("Third");
+
+        assertEquals("First", queue.poll(), "Order should be maintained; expected 'First'");
+        assertEquals("Second", queue.poll(), "Order should be maintained; expected 'Second'");
+        assertEquals("Third", queue.poll(), "Order should be maintained; expected 'Third'");
+    }
+
+    @Test
+    void testVariousDataTypes() {
+        GenericArrayListQueue<Double> queue = new GenericArrayListQueue<>();
+        queue.add(1.1);
+        queue.add(2.2);
+
+        assertEquals(1.1, queue.peek(), "Queue should handle Double data type correctly");
+        assertEquals(1.1, queue.poll(), "Poll should return correct Double value");
+        assertEquals(2.2, queue.peek(), "Peek should show next Double value in the queue");
+    }
+
+    @Test
+    void testEmptyPollAndPeekBehavior() {
+        GenericArrayListQueue<Integer> queue = new GenericArrayListQueue<>();
+        assertNull(queue.peek(), "Peek on an empty queue should return null");
+        assertNull(queue.poll(), "Poll on an empty queue should return null");
     }
 }