RE: (Java) Dealing With a Rogue Null Pointer Exception at Runtime
- From: "Michael Malver" <mmalver@xxxxxxxx>
- To: <programmingblind@xxxxxxxxxxxxx>
- Date: Tue, 11 Mar 2008 17:18:38 -0500
Look up the proper declaration for arrays. I think you have to explicitly
state the object type that is going to go in each element. I haven't had to
declare an array in quite some time, so I may be wrong about this.
-----Original Message-----
From: programmingblind-bounce@xxxxxxxxxxxxx
[mailto:programmingblind-bounce@xxxxxxxxxxxxx] On Behalf Of Jared Wright
Sent: Tuesday, March 11, 2008 3:20 AM
To: programmingblind@xxxxxxxxxxxxx
Subject: (Java) Dealing With a Rogue Null Pointer Exception at Runtime
Hi all, The following constructor keeps giving me a null pointer
exception if called at runtime. I guess the easiest place to start is
with a code exerpt. The context is that this class, cave, is made up of
an array of rooms. Each room has a number, three adjacent rooms, a
description, etc. It also tracks what the current room is, per the
user's direction in the larger scope of the program. The constructor
gets its info from a text file, and the amount of rooms in the cave
could vary based on this text file's contents. I think it is this
flexible length of the array of rooms for each cave object that's the
trouble spot, but beyond that I am admittedly stuck. Note that
TextReader serves much as the Scanner class would, this one just has a
couple of extra quirks that I like, thus I'm using it instead.
public class cave {
private int current; private int numrooms; // Variables for the current
room the user is in and the number of rooms in the cave.
private room myroom[]; // The array of room objects for the cave.
public cave(String filename) throws IOException {
current = 1;
TextReader file = new TextReader(new FileInputStream(filename)); //
numrooms=file.readInt(); // Reads in the first integer of the
file, which is the number of rooms the cave must hold.
myroom = new room[numrooms-1]; // Attempt to populate the myroom
array with the appropriate number of rooms. This is the line the
exception actually references, along with the line that called the
constructor (from another file).
}
The constructor actually goes on to fill the room objects with more
specific data (room number, description, etc.). Is there a better way
to go about this? Will I have to somehow explicitly define the array
length, or is there a way that the constructor can make the array the
appropriate size based on the data in the file? Might I be looking in
the wrong place for the source of this error?
More code available on request. I didn't want the snipet to get too big.
I hope I've made things clear, and thanks for any guidance, everyone.
Jared
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