a_124_StackL.java

public class a_124_StackL {
        
            static class Node {
                int data ;
                Node next;

                Node(int data) {
                    this.data = data ;
                    this.next = null ;
                }
            }
           
      static class Stack { 
            static Node head = null ;
        
            public static boolean isEmpty (){
                return head == null ;
            }
    
           // PUSH 
           public static void push(int data){
            Node newNode = new Node(data) ;
                if(isEmpty()){
                    head = newNode ;
                    return ;
                }

                newNode.next = head  ;
                head = newNode ;

           } 
    
           // POP
           public static int pop(){
            if(isEmpty()){
                return -1 ;
            }
            int top = head.data ;
            head = head.next   ;

            return top ;
           }
    
           // PEEK 
           public static int peek(){
            if(isEmpty()){
                return -1 ;
            }
            return head.data ;
           }
    
        }
        public static void main(String[] args) {
            Stack s = new Stack() ;
            s.push(1);
            s.push(2);
            s.push(3);
            s.push(4);
            s.push(5);
    
            while(!s.isEmpty()){
                System.out.println(s.peek());
                s.pop() ;
            }

        }
    }