Null Pointer Exception when adding items to ArrayList

[ShadowCopy]

Hi everyone,

I'm pretty new here, but I was hoping you could help me out with a little problem I seem to be having. As the title so aptly states, I'm receiving NullPointerException when I try to add an object to my ArrayList. I'm very new to ArrayLists so It's probably something ridiculously obvious, but your help is greatly appreciated.

Here's the code that I think matters. If you need more, let me know, I'll be happy to post it.

In the class Room.java

    // Holds the GameObjects that are present in the room
    private ArrayList<GameObject> roomObjects;
 
   ...

    // Public method to add objects to the roomObjects ArrayList
    public void addRoomObject(GameObject obj){
        roomObjects.add(obj); // <- NullPointerException
    }

In the main class

        // Create a test object
        GameObject testObj = new GameObject();

        testObj.setSDesc("A shiny ruby has been carelessly discarded here.");

        // Add the object to the room
        test.addRoomObject(testObj); // <- NullPointerException

The compiler (NetBeans) shows me two locations for the exception, which I commented in the above code samples. Again, thanks so much for your help.

[r035198x]

 private ArrayList<GameObject> roomObjects;

does not create an ArrayList object. It creates a reference to an ArrayList object. At this point the reference is initialized as pointing to null (the default value for reference types). You need to initialize roomObjects by using the new operator

roomObjects = new ArrayList<GameObject>();

[ShadowCopy]

Ok, well I figured it out. It was a very noobish mistake and I shouldn't be up at 3:30 in the morning coding, but I forgot to actually create the arraylists lol. I just created the references without creating them.

    // Holds the GameObjects that are present in the room
    private ArrayList<GameObject> roomObjects = new ArrayList();

    // Holds the RoomExits that are present in the room
    private ArrayList<RoomExits> roomExits = new ArrayList();

That fixed that problem. Also in my output method I was outputting the object itself, and not the objects short description.

        Iterator<GameObject> itr = roomObjects.iterator();
        System.out.println();
        // Print the contents

        while (itr.hasNext()){
            System.out.println(itr.next().getSDesc()); // Didn't have the .getSDesc
        }

So thanks anyhow :) Figured I'd at least post this in case someone else ran into a similar problem.

[ShadowCopy]

 private ArrayList<GameObject> roomObjects;

does not create an ArrayList object. It creates a reference to an ArrayList object. At this point the reference is initialized as pointing to null (the default value for reference types). You need to initialize roomObjects by using the new operator

roomObjects = new ArrayList<GameObject>();

Thank you very much. I figured it out, stupid mistake :)