Linked List

[seanfmglobal]

When adding nodes to your linked list are you inserting everything to the tail are to the head? So traversing through the list is it LIFO or FIFO???? Thanks

[JosAH]

It also depends from which side the nodes are deleted ...

kind regards,

Jos

ps Why is this in the advanced section?

[DIego912]

Both... It depends on the observer's viewpoint...

[seanfmglobal]

Ok here it is, I have a node....

package listwnodes;

public class Node<T> {

	private Node<T> next;
	private Node<T> prev;
	private T element;
	
	public Node(){
		element = null;
		next = prev = null;
	}
	
	public Node(T ele){
		this.element = ele;
		next = prev = null;
		}
	
	public void setprev(Node<T> node){
		this.prev = node;
	}
	
	public void setnext(Node<T> next){
		this.next = next;
	}
	
	public Node<T> getNext(){
		return this.next;
	}
	
	public Node<T> getPrev(){
		return this.prev;
	}
	
	public String testString(){
		String s = "Previous Element: "+getNext().element+"\nThis element: "+element+"\n";
		return s;
	}
	
}

I have a list....

package listwnodes;

public class SuperList<T> implements SeanList<T>{

	private Node<T> head;
	private Node<T> tail;
	private int count;
	
		
	@Override
	public void addElement(T ele) {
		// TODO Add element to end older elements go to the front
		Node<T> tempNode;
		tempNode = new Node<T>(ele);
		if(count == 0){
			
			tempNode.setprev(tail);
			tempNode.setnext(head);
			head.setprev(tempNode);
			tail.setnext(tempNode);
			count++;
		}	else{
			tempNode.setprev(tail);
			tempNode.setnext(tail.getNext());
			tail.setnext(tempNode);
			count++;
			System.out.println(tempNode.testString());
		}
		
		
	}

	@Override
	public T getElement(int i) {
		// TODO Auto-generated method stub
		return null;
	}

	@Override
	public void removeElement(T ele) {
		// TODO Auto-generated method stub
		
	}

	@Override
	public T getElementFromI(int index) {
		// TODO Auto-generated method stub
		return null;
	}

	@Override
	public void RemoveElement(T ele) {
		// TODO Auto-generated method stub
		
	}
	
	public T viewElement(){
		Node<T> temp = new Node<T>();
		return null ;
	}
	
	public int compareTo(T ele){
		return 0;
	}

	

}

and my main

package mainStuff;

import java.util.Random;

import listwnodes.SeanList;
import listwnodes.SuperList;

public class MainListTest {

	public static void main(String[] args){
	//	SeanList<Integer> myList = new SuperList<Integer>();
		SuperList<Integer> myList = new SuperList<Integer>();
		//SuperList<Comparable<T>>
		Random rand = new Random();
		
		for (int i = 0; i < 10; i++) {
			myList.addElement((Integer) rand.nextInt(50)+1);
		}
	}
}

For some reason when trying to add elements to my list I get a null pointer exception at the line in my SuperList class "head.setprev(tempNode);". Can anyone explain why please. Thank you guys very much.