public class LinkedStack<T> implements Stack<T> {

private Node<T> top;

public LinkedStack() {

top = null;

}

@Override

public void push(T item) {

top = new Node<T>(item, top);

}

@Override

public T pop() throws StackUnderflowException{

if(top != null) {

Node<T> oldTop = top;

top = top.getNext();

return oldTop.getValue();

} else {

throw new StackUnderflowException("trying to pop from an empty stack\n");

}

}

@Override

public T peek() throws StackUnderflowException {

if(top != null) {

return top.getValue();

} else {

throw new StackUnderflowException("trying to peek from an empty stackn");

}

}

public boolean isEmpty() {

return top == null;

}

//method to modified the output information

public String toString(){

String stackString =" ";

Node<T> node;

node =top;

while (node != null) {

//stack should the order starting from the top

stackString =node.getValue() +" "+stackString+" ";

node =node.getNext();

}

return stackString;

}

@SuppressWarnings("hiding")

private class Node<T> {

private T value;

private Node<T> next;

public T getValue() {

return value;

}

@SuppressWarnings("unused")

public void setValue(T value) {

this.value = value;

}

public Node<T> getNext() {

return next;

}

@SuppressWarnings("unused")

public void setNext(Node<T> next) {

this.next = next;

}

public Node(T value, Node<T> next) {

super();

this.value = value;

this.next = next;

}

}

}