Thread: can't figure whats wrong with my add method?? help!

I have a interface called "ListInterface", a class called "LList" and a main "LListTest"

my an add method that is not running.

public class LList<T> implements ListInterface<T> {
 
	private Node firstNode;	// reference to first node
	private int length;		// number of entries in list
 
	public LList(){
		clear();
	}
 
	public final void clear(){
		firstNode = null;
		length = 0;
	}
 
	@Override
	public boolean add(T newEntry) {
		Node newNode = new Node(newEntry);
		if (isEmpty()){
			firstNode = newNode;
		}else{
			Node lastNode = getNodeAt(length);
			lastNode.next = newNode;	// make last node reference new node
		}
		length++;
		return true;
	}
 
	@Override
	public boolean add(int newPosition, T newEntry) {
		boolean isSuccessful = true;
		if (1 <= newPosition && newPosition <= length+1){
			Node newNode = new Node(newEntry);
			if (isEmpty() || newPosition == 1){	// case 1
				newNode.next = firstNode;
				firstNode = newNode;
			}else{								// case 2
				Node nodeBefore = getNodeAt(newPosition-1);
				Node nodeAfter = nodeBefore.next;
				newNode.next = nodeAfter;
				nodeBefore.next = newNode;
			}
			length++;
		}else{
			isSuccessful = false;
		}
		return isSuccessful;
	}
 
	@Override
	public void display() {
		Node currentNode = firstNode;
		while(currentNode != null){
			System.out.println(currentNode.data);
			currentNode = currentNode.next;
		}
	}
 
	@Override
	public boolean isEmpty() {
		boolean result;
		if (length == 0){
			assert firstNode == null : "length = 0 but firstNode is not null";
			result = true;
		}else{
			assert firstNode != null : "length not 0 but firstNode is null";
			result = false;
		}
		return result;
	}
	/**	Task: Returns a reference to the node at a given position.
	 * 	Precondition: List is not empty; 1 <= givenPosition <= length.
	 * @param givenPosition
	 * @return
	 */
	private Node getNodeAt(int givenPosition){
		assert (!isEmpty() && 1 <= givenPosition && givenPosition <= length);
		Node currentNode = firstNode;
		for (int counter = 1; counter < givenPosition; counter++){
			currentNode = currentNode.next;
		}
		assert currentNode != null;
		return currentNode;
	}
 
	private class Node //private inner class
	{	
		private T data;
		private Node next;
 
		private Node(T dataPortion){
			data = dataPortion;
			next = null;
		}
 
		private Node(T dataPortion, Node nextNode){
			data = dataPortion;
			next = nextNode;
		}
	}// end Node
 
}

here is the interface "ListInterface" (no issues with this part of the code) I am giving it just in case you would like to run the program yourself.

/** An interface for the ADT list.
 * Entries in the list have positions that begin with 1.
 */
public interface ListInterface<T> 
{
	/** Task: Adds a new entry to the end of the list.
	 * 		  Entries currently in the list are unaffected.
	 * 		  The list's size is increased by 1.
	 * 	@param newEntry	the object to be added as a new entry
	 * 	@return true if the addition is successful, or false if the list is full */
	public boolean add(T newEntry);
 
	/** Task:	Adds a new entry at a specified position within the list.
	 * 			Entries originally at and above the specified position are at the 
	 * 			next higher position within the list.
	 * 			The list's size is increased by 1.
	 *  @param 	newPosition		an integer that specifies the desired position of the new entry
	 *  @param	newEntry		the object to be added as a new entry
	 *  @return	true if the addition is successful, or false if either the list is full, newPosition < 1, 
	 *  		or newPosition > getLength()+1	*/
	public boolean add(int newPosition, T newEntry);
 
 
	/** Task: Remmoves all entries from the list. */
	public void clear();
 
	/**	Task: Sees whether the list is empty
	 * @return	true if the list is empty, false if the list is not empty */
	public boolean isEmpty();
 
	/**	Task: 	Displays all entries that are in the list, one per line, in the order in which they 
	 * 			occured in the list */
	public void display();
 
}

and here is my Main: the line of code: list.add("bobby");

is giving me an issue.

 
public class LListTest {
 
	/**
	 * @param args
	 */
	public static void main(String[] args) {
		LList<String> list = new LList<String>();
 
 
		list.add("bobby");
		list.add("sue");
		list.add("john");
		list.add(2,"joey");
		list.add("andres");
		list.display();
	}
 
}

Yeah... I'd recommend surrounding relevant code in code tags, (as found in my signature) and removing a lot of that unnecessary code before an angry mod stamps all over you

Could you please just a short code snip-it where you believe a problem is occurring, say what the problem is, how it's behaving and how it's supposed to be behaving and you will greatly increase your chances of being helped.