Enhance docs, add tests in StackArrayList (#6020)

src/main/java/com/thealgorithms/datastructures/stacks/StackArrayList.java

@@ -4,23 +4,41 @@ import java.util.ArrayList;
 import java.util.EmptyStackException;
 
 /**
- * This class implements a Stack using an ArrayList.
+ * A stack implementation backed by an {@link ArrayList}, offering dynamic resizing
+ * and LIFO (Last-In-First-Out) behavior.
  *
- * @param <T> the type of elements in this stack
+ * <p>The stack grows dynamically as elements are added, and elements are removed
+ * in reverse order of their addition.
+ *
+ * @param <T> the type of elements stored in this stack
  */
 public class StackArrayList<T> implements Stack<T> {
 
     private final ArrayList<T> stack;
 
+    /**
+     * Constructs an empty stack.
+     */
     public StackArrayList() {
         stack = new ArrayList<>();
     }
 
+    /**
+     * Adds an element to the top of the stack.
+     *
+     * @param value the element to be added
+     */
     @Override
     public void push(T value) {
         stack.add(value);
     }
 
+    /**
+     * Removes and returns the element from the top of the stack.
+     *
+     * @return the element removed from the top of the stack
+     * @throws EmptyStackException if the stack is empty
+     */
     @Override
     public T pop() {
         if (isEmpty()) {
@@ -29,6 +47,12 @@ public class StackArrayList<T> implements Stack<T> {
         return stack.removeLast();
     }
 
+    /**
+     * Returns the element at the top of the stack without removing it.
+     *
+     * @return the top element of the stack
+     * @throws EmptyStackException if the stack is empty
+     */
     @Override
     public T peek() {
         if (isEmpty()) {
@@ -37,16 +61,29 @@ public class StackArrayList<T> implements Stack<T> {
         return stack.getLast();
     }
 
+    /**
+     * Checks if the stack is empty.
+     *
+     * @return {@code true} if the stack is empty, {@code false} otherwise
+     */
     @Override
     public boolean isEmpty() {
         return stack.isEmpty();
     }
 
+    /**
+     * Empties the stack, removing all elements.
+     */
     @Override
     public void makeEmpty() {
         stack.clear();
     }
 
+    /**
+     * Returns the number of elements in the stack.
+     *
+     * @return the current size of the stack
+     */
     @Override
     public int size() {
         return stack.size();