StackUsingAL.java

import java.util.*;
public class StackUsingAL{
    public static class Stack{
        static ArrayList<Integer> s = new ArrayList<>();
        public static boolean isEmpty(){
            return s.size()==0;
        }
        public static void push(int data){
            s.add(data);
        }
        public static int pop(){
            if (isEmpty()){
                return -1;
            }
            int top=s.get(s.size()-1);
            s.remove(s.size()-1);
            return top;
        }
        public static int peek(){
            if (isEmpty()){
                return -1;
            }
            return s.get(s.size()-1);
        }
    }
    public static void main(String[] args) {
        Stack.push(30);
        Stack.push(20);
        Stack.push(30);
        while(!Stack.isEmpty()){
            System.out.println("Top: " + Stack.peek());
            Stack.pop();
        }
    }
}