覆盖二维数组列表中的一行

Question

I have a 2D arraylist containing 4 cols. I want to add a 5 th column to this arraylist. the fourth col is a set of values based on which the result is to be added as the 5th column. If 1st row has 4th element as 0 then the fifth column will have a result string "Failure"

Is it ok to use a 1D arraylist to get all the elements of the 2D arraylist and add the 5th element to it and then overwrite the 2D with the 1D arraylist items OR Is there a way we can directly append to the 2D arraylist using the index() and indexOF()?

Will appreciate it if someone can help me out with this.

Answer 1

Java doesn't support first-class multi-dimensional arrays. A two dimensional array is an 'array of arrays'. Java also does not support resizing of arrays.

Assuming you've already got data in your String[][] table:

String[][] table = /* init from somewhere */;

for (int i = 0; i < table.length; i++) {
   String[] row = table[i];
   assert (row.length == 4);
   String[] newRow = Arrays.copyOf(row, 5);
   assert (newRow.length == 5);
   newRow[4] = "Failure";
   table[i] = newRow;
}

That's approximately how you'd handle adding a column. Notice that Arrays.copyOf() is much better than copying the array's contents 'by hand'.

(note: when you run this sample, use the -ea flag to the JVM so that the assertions fire)

Answer 2

You should be able to use ArrayList#add

for(ArrayList<Object> a: in aa){
    a.add(a.get(3) == 0 ? "failure" : "success")
}