StackOfLinkedList.java

/**
 * @author Varun Upadhyay (https://github.com/varunu28)
 */

// An implementation of a Stack using a Linked List

class StackOfLinkedList {

 public static void main(String[] args) {

 LinkedListStack stack = new LinkedListStack();
 stack.push(1);
 stack.push(2);
 stack.push(3);
 stack.push(4);
 stack.push(5);

 stack.printStack();

 System.out.println("Size of stack currently is: " + stack.getSize());

 stack.pop();
 stack.pop();

 System.out.println("Top element of stack currently is: " + stack.peek());
 }
}

// A node class

class Node {
 public int data;
 public Node next;

 public Node(int data) {
 this.data = data;
 this.next = null;
 }
}

/**
 * A class which implements a stack using a linked list
 * <p>
 * Contains all the stack methods : push, pop, printStack, isEmpty
 **/

class LinkedListStack {

 Node head = null;

 public void push(int x) {
 Node n = new Node(x);
 if (head == null) {
 head = n;
 } else {
 Node temp = head;
 n.next = temp;
 head = n;
 }
 }

 public void pop() {
 if (head == null) {
 System.out.println("Empty stack. Nothing to pop");
 }

 Node temp = head;
 head = head.next;
 System.out.println("Popped element is: " + temp.data);
 }

 public int peek() {
 if (head == null) {
 return -1;
 }
 return head.data;
 }

 public void printStack() {
 Node temp = head;
 System.out.println("Stack is printed as below: ");
 while (temp != null) {
 if (temp.next == null) {
 System.out.print(temp.data);
 } else {
 System.out.print(temp.data + " -> ");
 }
 temp = temp.next;
 }
 System.out.println();
 }

 public boolean isEmpty() {
 return head == null;
 }

 public int getSize() {
 if (head == null)
 return 0;
 else {
 int size = 1;
 Node temp = head;
 while (temp.next != null) {
 temp = temp.next;
 size++;
 }
 return size;
 }
 }
}