stack (thing)

No code here? Come on people! I can offer up my Java implementation of a Stack, which is based on the Doubly Linked List (which I have also noded). This should help anyone struggling along (like I was) in a Data Structures class. Even if you aren't using Java, the code is well commented for easy porting to other languages. Note: this Stack takes objects; not primitive types. Enjoy!

//************************************************************
// This class defnines the Stack structure.
// It is based on a Linked List.
//************************************************************

public class MyStack extends ListClass
{

//************************************************************
// Declares an integer to hold the number of elements on the
// stack.
//************************************************************

	private int numOnStack = 0;

//************************************************************
// This is the default constructor for the stack class.
// It assigns all omnipresent nodes to null.
//************************************************************

	public MyStack()
	{
	start = current = end = null;
	}

//************************************************************
// This method, push() takes an object and adds it to the 
// stack. It also increments numOnStack.
//************************************************************

	public void push(Object oneObject)
	{
		addBefore(oneObject);
		numOnStack++;
	}

//************************************************************
// This method, pop() removes the top element from the stack
// and returns the contents to the calling object. It also
// decrements numOnStack.
//************************************************************

	public Object pop()
	{
		
		Object o = null;
		current = start;

		if(this.isEmpty() == false)
		{
			if(start.getNext() == null)
			{
				o = start.getObject();
				current = start = end = null;
				numOnStack--;
				return(o);
			}
			else
			{
				o = start.getObject();
				start = current = start.getNext();
				numOnStack--;
				return(o);
			}
		}
		return("If you see this, there is an error.");
	}

//************************************************************
// This method, getNumOnStack() returns the number of
// elements on the stack.
//************************************************************

	public int getNumOnStack()
	{
	return numOnStack;
	}

//************************************************************
// This method, isEmpty() determines if the stack is empty,
// using the int value of numOnStack as an indicator.
//************************************************************

	public boolean isEmpty()
	{
		if(numOnStack == 0)
			return true;
		else
			return false;
	}
}