2D array[row][] = str.split("\t") not behaving as expected

Question

Whilst I can get it to work on a 1 dimension array (String array[] = str.split(blah)), I have trouble on 2D arrays. I'm using a loop that goes through each row of the 2D array and assigns it whatever str.split(\t) has.

For example:

John\tSmith\t23
James\tJones\t21

My 2D array will look like this: {{John, Smith, 23}, {James, Jones, 21}} I've only begun Java so I'm not too sure about some of the syntax for 2D arrays.

EDIT: Some code as requested

String str;
int row = 0;
String array[][];
while ((str = br.readLine()) != null)   {
    array[row] = str.split("\t");
    System.out.println(array[row][0]);
    row++;
}

What have you tried so far? What error are you getting? Can we see some code please? — Brian, Sep 11 '12 at 15:50
Do you mean `array[0] = "John\tSmith\t23".split("\t");`? Are you getting a NullPointerException? If so did you allocate any space to the array? — Peter Lawrey, Sep 11 '12 at 15:52
You cave to initialize your array before using it. You just declared it so far. — Baz, Sep 11 '12 at 15:54
@Peter and Baz What if the data I want to put in the array is dynamic? This was my previous question on SO it might add some context: http://stackoverflow.com/questions/12370657/convert-a-string-last-tfirst-tage-to-an-array-with-elements-last-first-age — meiryo, Sep 11 '12 at 15:54
@meiryo Then don't use arrays. Use a `List` instead, like [`ArrayList`](http://docs.oracle.com/javase/7/docs/api/java/util/ArrayList.html). — Baz, Sep 11 '12 at 15:56

Eng.Fouad · Accepted Answer · 2012-09-11T16:02:58.563

You need to initialize your array as follows:

int rowCount = ...;
String array[][] = new String[rowCount][];

or in case you don't know the number of rows, you may use ArrayList instead:

List<String[]> list = new ArrayList<String[]>();
String str;
while((str = br.readLine()) != null)
{
    String[] array = str.split("\t");
    list.add(array);
}
String[][] array2D = new String[list.size()][];
list.toArray(array2D);

score 1 · Answer 2 · edited May 23 '17 at 12:21

1

You have to use str.split("\\\\t"); The split method accepts a regular expression.
Check this post for more details

edited May 23 '17 at 12:21

Community

1
1

answered Sep 11 '12 at 16:01

basiljames

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score 1 · Answer 3 · answered Sep 11 '12 at 16:02

Your String array[][] must be initialized before use it.

If you can, move your code to use Lists to make it work:

List<List<String>> array = new ArrayList<List<String>>();
while ((str = br.readLine()) != null)   {
    array.add(Arrays.asList(str.split("\t")));
}

In case you must not use List, then initialize your array

final int SIZE = ...; //some value that would be the max size of the array of arrays
String array[][] = new String[SIZE][];

2D array[row][] = str.split("\t") not behaving as expected

3 Answers3