Stack.java

public class Stack{
  
  private StackNode topOfStack;
  
  private class StackNode{
    private Object element;
    private StackNode next;
    
    private StackNode(Object e, StackNode n){
      element = e;
      next = n;
    }
  }
  
  public Stack(){
    topOfStack = null;
  }
  
  public boolean isEmpty(){
    return topOfStack==null;
  }
  
  public void makeEmpty(){
    topOfStack=null;
  }
  
}