package DataStructures.Stacks;

import java.util.ArrayList;

/**
 * This class implements a Stack using an ArrayList.
 * <p>
 * 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.
 * <p>
 * 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();
 
 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);
 }
}