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(); 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 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); } }