Stack.java

package com.examplehub.datastructures.stack;

import java.util.ArrayList;
import java.util.EmptyStackException;

public class Stack<E> {

  /** Stack which stores elements. */
  private ArrayList<E> stack;

  public Stack() {
    this.stack = new ArrayList<>();
  }

  /**
   * Pushes an item onto the top of this stack.
   *
   * @param item the item to be pushed onto this stack.
   * @return the {@code item} argument.
   */
  public E push(E item) {
    stack.add(item);
    return item;
  }

  /**
   * Removes the object at the top of this stack and returns that object as the value of this
   * function.
   *
   * @return The object at the top of this stack (the last pushed item).
   */
  public E pop() {
    if (empty()) {
      throw new EmptyStackException();
    }
    return stack.remove(stack.size() - 1);
  }

  /**
   * Looks at the object at the top of this stack without removing it from the stack.
   *
   * @return the object at the top of this stack (the last item pushed).
   * @throws EmptyStackException if the stack is empty.
   */
  public E peek() {
    if (empty()) {
      throw new EmptyStackException();
    }
    return stack.get(size() - 1);
  }

  /**
   * Returns the number of elements in this stack.
   *
   * @return the number of elements in this stack.
   */
  int size() {
    return stack.size();
  }

  /**
   * Returns {@code true} if this stack contains no elements.
   *
   * @return {@code true} if this stack contains no elements, otherwise {@code false}.
   */
  public boolean empty() {
    return size() == 0;
  }

  /** Clear all elements in the stack. */
  public void clear() {
    stack.clear();
  }

  @Override
  public String toString() {
    return stack.toString();
  }
}