Creating a generic stack in generic stack class

I'm trying to teach myself some java and im stuck on a problem that seems kind of easy but i still don't seem to find a solution.

What I have so far:

Interface:

public interface ADTStack<T> { public boolean isEmpty(); public void push(T element); public T top() throws IllegalStateException; public void pop() throws IllegalStateException; } 

Class Stack:

public class Stack<T> implements ADTStack<T> { private java.util.LinkedList<T> data; public Stack() { data = new java.util.LinkedList<T>(); } @Override public boolean isEmpty() { return data.isEmpty(); } @Override public void push(T element) { data.add(0, element); } @Override public T top() throws IllegalStateException { if (isEmpty()) { throw new IllegalStateException("Stack is emtpy."); } return data.getFirst(); } @Override public void pop() throws IllegalStateException { if (isEmpty()) { throw new IllegalStateException("Stack is empty."); } data.remove(0); } 

Alright , so here is what I'm trying to do. I'm trying to write a methode equals to compare two Stacks. My idea was to use a third Stack to be able to bring both stacks into their original state after comparing them.

Here's what I have:

 Stack supportStack = new Stack(); public boolean equals(ADTStack<T> s){ if (data.isEmpty() != s.isEmpty()){ return false; } if (data.isEmpty() && s.isEmpty()){ return true; } T element_a = this.top(); T element_b = s.top(); if( (element_a ==null && (element_b !=null) || !element_a.equals(element_b) || element_a != null && element_b == null)){ return false; } data.pop(); s.pop(); supportStack.push(element_a); boolean result = data.equals(s); while (!supportStack.isEmpty()){ data.push(supportStack.top()); s.push(supportStack.top()); supportStack.pop(); } return result; } 

I get a lot of errors when I compile the code and it seems that something is wrong with :

Stack supportStack = new Stack(); 

I don't really know what's wrong and how to solve the error. I made a runner-class and I tried the constructor and it worked so I'm confused at what's wrong.

public class Runner { public static void main(String[] args){ Stack test = new Stack(); test.push(12); System.out.println(test.top()); } } 

I gladly take any advice or constructive criticism since I'm teaching myself and if anything seems unclear feel free to ask.