Stack using Linked List

LinkedStack.java

class Node {
	String data;
	Node next;
	
	Node(String data) {
		this.data = data;
		next = null;
	}
}

class Stack {
	private Node top = null;
	private int counter = 0;
	
	public void push(String value) {
		Node newNode = new Node(value);
		
		if (top == null) {
			top = newNode;
		} else {
			newNode.next = top;
			top = newNode;
		}
		
		counter++;
	}
	
	public void pop() {
		if (!isEmpty()) {
			System.out.println(top.data);
			top = top.next;
		} else {
			System.out.println("stack underflow");
		}
		
		counter--;
	}
	
	public void peek() {
		System.out.println(!isEmpty() ? top.data : "stack underflow");
	}
	
	public boolean isEmpty() {
		return (top == null);
	}
	
	public void print() {
		Node temp = top;
		
		for (int i=0; i<counter; i++) {
			System.out.print(top.data + ", ");
			top = top.next;
		}
		
		top = temp;
	}
}

public class LinkedStack {
	public static void main(String[] args) {
		Stack s = new Stack();
		s.push("D1");
		s.push("D2");
		s.push("D3");
		s.push("D4");
		s.push("D5");
		s.push("D6");
		s.push("D7");
		
		s.pop();
		s.peek();
	}
}