Why can I not add this object to array list?

Question

Hello I have the following code:

    java.util.Date date = new java.util.Date();

    ArrayList<Worker> workerList = null;

            //Create Worker
            System.out.println ("You have selected create worker. \n" + "please enter a name for the worker.\n");

            //Create new worker object
            scanner.nextLine();
            String tName = scanner.nextLine();

            Worker newWorker = new Worker (tName, date, 0); 

            workerList.add(newWorker);

            wCurrent = newWorker;

and

Worker (String s, Date d, int i){
    workerName = s;
    dateEmployed = d;
    jobsCompleted = i;
}

However it always crashes at the workerList.add, where is my error? Netbeans says "Null Pointer Defference" I do not know what that means... Please help

EDIT! Thanks it fixed it!

Just another quick question

I have also got

   public String toString(){
       return "The worker " + workerName + " has completed "+ jobsCompleted + " jobs";
    }

But but everytime I am calling the toString method it crashes. This is after I create the object.

You've forgotten to assign your list to a List instance: `List workerList = new ArrayList();` — Konstantin Yovkov, Sep 03 '15 at 10:59
Why don't you help me instead of saying possible duplicate? You're not doing anybody good @NamanGala — J. Doh, Sep 03 '15 at 11:28
We are here to help only. That's why I gave you good stuff from stack overflow which I think you did not refer before. It will clear many concepts. And you can check out answers given by people from SO below! — Naman Gala, Sep 03 '15 at 11:30

score 4 · Accepted Answer · answered Sep 03 '15 at 10:59

 ArrayList<Worker> workerList = null;

You initialized it to null. Hence the crash. You need to initialize properly

 ArrayList<Worker> workerList = new ArrayList<Worker>();

And even better with interface programming (Instead of ArrayList on left hand side, declare a List)

 List<Worker> workerList = new ArrayList<Worker>();

score 4 · Answer 2 · edited May 23 '17 at 12:22

You only need to initialize your list. You create a variable ArrayList<Worker> workerList and fill it with null. Do List<Worker> workerList = new ArrayList<>(); for a correct initialization when declaration or workerList = new ArrayList<>(); if you want to initialize it later after the declaration, which is often usefull. You can read What is a NullPointerException, and how do I fix it? for further information.

Why can I not add this object to array list?

2 Answers2