2

First of all, Beginner here.

I'm using this code.

class MDArrays { public static void main(String[] args) { int[][] x; int t=2; x = new int[2][3]; for(int i=0; i<=1; i++) { for(int j=0; i<=2; j++) { x[i][j] = t; t += 2; System.out.println(x[i][j]); } } } }

It compiles perfectly, but when running it, after displaying 3 numbers correctly I'm getting the following error.

Exception in thread "main" java.Lang.ArrayindexOutOfBoundsException : 3 at MDArrays.main(MDArrays.java:13)

Where am I going wrong?

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1
  • +1 - Though it was a simple mistake, the question has good grammar, and is clearly written. Commented Jul 9, 2010 at 20:54

3 Answers 3

Reset to default
8

You are incrementing j while checking against i.

for(int j=0; i<=2; j++)

j will keep incrementing which will eventually give you an IndexOutOfBoundsException

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1 Comment

Cannot believe I mistyped it. This is one bad question.
3 
for(int j=0; i<=2; j++) {

Is your problem. Try:

for(int j=0; j<=2; j++) {
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3

I would write it like this:

class MDArrays { private static final int ROWS; private static final int COLS; private static final int START_VALUE; private static final int INC_VALUE; static { ROWS = 2; COLS = 3; START_VALUE = 2; INC_VALUE = 2; } public static void main(String[] args) { final int[][] x; int t; x = new int[ROWS][COLS]; t = START_VALUE; for(int row = 0; row < x.length; row++) { for(int col = 0; col < x[row].length; col++) { x[row][col] = t; t += INC_VALUE; System.out.println(x[row][col]); } } } }

The major difference is that I use the .length member rather than hard coded values. That way if I change it to x = new int[3][2]; then the code magically works and stays within its bounds.

The other big difference is that I use row/col instead of i/j. i/j are fine (and traditional) but I find when dealing with arrays of arrays (Java doesn't actually have multi-dimensional arrays) that it is easier to keep track of things if I use the more meaningful row/col (helps prevent you from doing things like for(int col = 0; row < x.length; col++)... which, incidentally, is the bug you have.

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4 Comments

I would also like to get rid of those magic numbers (2 and 3) using private static finals.
yeah, I was going to do that too, but didn't want to make it soooo different - but given you feel that way too I'll do it!
Did not you mean x.length ? Currently at row: for(int row = 0; row < row.length; row++) you get error: The primitive type int of row does not have a field length MDArrays.java /StackOverflow/src line 24 Java Problem
+1 Good point. Many beginners overlook healthy variable names.

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