Question

I’m working on a text-based adventure game project. It involves rooms with items in them and navigating from room to room. There’s a class called Item and this larger class called Room. All of my methods seem to work except addNeighbor (and presumably getNeighbor too, then.) I created a room with an item and that worked just fine, and I created a second room, but when I tried to add a neighbor it crashed and gave me a Null Pointer Exception. What am I doing wrong here?

public class Room
{
    private String roomDescription;
    private Item item;
    private HashMap <String, Room> myNeighbors;

    public Room (String pDescription){
        roomDescription = pDescription;
        item = null;
    }

    public Room (String pDescription, Item pItem){
        roomDescription = pDescription;
        item = pItem;
    }

    public String getRoomDescription(){
        return roomDescription;
    }

    public Item getItem(){
        return item;
    }

    public void addItem (Item i){
        item = i;
    }

    public boolean hasItem(){
        if(item != null){
            return true;
        }else{
            return false;
        }
    }

    public void addNeighbor (String pDirection, Room r){
        myNeighbors.put(pDirection, r);
    }

    public Room getNeighbor (String pDirection){
        return myNeighbors.get(pDirection);
    }

    public Item removeItem(){
        item = null;
        return item;
    }

    public String getLongDescription(){
        String longDescription = "You are at " + roomDescription + "You see " + item;
        return longDescription;
    }
}

Answer 1

You’ve never initialised myNeighbors; it’s just a reference that points to nowhere.

Consider private HashMap <String, Room> myNeighbors = new HashMap<String,Room>();.