Multi-dimensional arrays: Variable length row?

Question

It is possible to do variable length columns such as:

private int k[][] = new int[3][];

for(int i = 0; i < k.length; i++) {
   k[i] = new int[i+1];
}

I was wondering if it was possible to do variable length rows, if you know the length of a column?:

private int k[][] = new int[][5];

for(int i = 0; i < k.length; i++) {
   // How would you do this?
}

Thank you.

Arrays in Java are always of a fixed length. If you need something variable in size, use ArrayList. It can also be nested, if you really have to do that. — Till Helge, May 22 '13 at 11:23
Compiler: Cannot specify an array dimension after an empty dimension — johnchen902, May 22 '13 at 11:24

score 4 · Accepted Answer · answered May 22 '13 at 11:23

You can't, basically. A "multi-dimensional" array is just an array of arrays. So you have to know the size of the "outer" array to start with, in order to create it.

So your options are:

Use the array in an inverted way as array[column][row] instead of array[row][column]
Use a list instead, so you can add new rows as you go:
```
List<Object[]> rows = new ArrayList<Object[]>();
for (SomeData data : someSource) {
    Object[] row = new Object[5];
    ...
    rows.add(row);
}
```
(Or even better, encapsulate your concept of a "row" in a separate class, so you have a List<Row>.)

Multi-dimensional arrays: Variable length row?

1 Answers1