Java/DataStructures/Stacks/StackArrayList.java

import java.util.ArrayList;

/**
 * This class implements a Stack using an ArrayList.
 *
 * A stack is exactly what it sounds like. An element gets added to the top of
 * the stack and only the element on the top may be removed.
 *
 * This is an ArrayList Implementation of a stack, where size is not
 * a problem we can extend the stack as much as we want.
 *
 * @author Unknown
 *
 */
public class StackArrayList{

  /**
   * Main method
   *
   * @param args Command line arguments
   */
  public static void main(String[] args) {
    StackArrayList myStackArrayList = new StackArrayList(); //Declare a stack of maximum size 4
    //Populate the stack
    myStackArrayList.push(5);
    myStackArrayList.push(8);
    myStackArrayList.push(2);
    myStackArrayList.push(9);

    System.out.println("*********************Stack List Implementation*********************");
    System.out.println(myStackArrayList.isEmpty()); //will print false
    System.out.println(myStackArrayList.peek()); //will print 9
    System.out.println(myStackArrayList.pop()); //will print 9
    System.out.println(myStackArrayList.peek()); // will print 2
    System.out.println(myStackArrayList.pop()); //will print 2
  }

  /** ArrayList representation of the stack */
  private ArrayList<Integer> stackList;

  /**
   * Constructor
   */
  public StackArrayList(){
    stackList = new ArrayList<>();
  }

  /**
   * Adds value to the end of list which
   * is the top for stack
   *
   * @param value value to be added
   */
  public void push(int value){
    stackList.add(value);
  }

  /**
   * Pops last element of list which is indeed
   * the top for Stack
   *
   * @return Element popped
   */
  public int pop(){

    if(!isEmpty()){ // checks for an empty Stack

      int popValue=stackList.get(stackList.size()-1);
      stackList.remove(stackList.size()-1);  //removes the poped element from the list
      return popValue;
    }

    System.out.print("The stack is already empty  ");
    return -1;
  }

  /**
   * Checks for empty Stack
   *
   * @return true if stack is empty
   */
  public boolean isEmpty(){
    return stackList.isEmpty();
  }

  /**
   * Top element of stack
   *
   * @return top element of stack
   */
  public int peek(){
    return stackList.get(stackList.size()-1);
  }
}