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);

}

}