Java, how to get a collection of byte from a byte array

Question

This question may seems unique but I am having difficulties on solving it.

I have a byte array (a DW per row) and trying to get the byte value for every 9 bytes. Here is how the byte array looks like:

0   1   2   3
4   5   6   7
8|  9   10  11
12  13  14  15
16  17| 18  19
20  21  22  23
24  25  26| 27
28  29  30  31
32  33  34  35|
.......

Here is a defined function that I need to use to get the value from the above patent:

getValue(int DWOffset, int highBit, int lowBit)

//DWOffset indicates the row of the data.
//highBit indicates the ending bit
//lowBit indicates the starting bit

My question is how to get every 9 bytes from the data (where the | appears) by using for loop? The data length can be found out by using

data.getLength();    //which returns the total number of bytes in the data

So far, I can get value on the first two row:

for(int i = 0; i < data.getLength()/(4*2); i++){
    getValue(i*2, 31, 0);         //DW i
    getValue(i*2 + 1, 31, 0);     //DW i+1
} 

Answer 1

Part of the problem is that you seem to be mixing paradigms, conceptually looking at it as both a 2-dimensional and a 1-dimensional array. Looking at it as 2-dimensional, you need a getValue(int row, int column) that returns a single byte. Then you can do something like this:

final int TOTAL_BYTES_TO_INCLUDE = 9;

byte[] byteArray[] = new byte[TOTAL_BYTES_TO_INCLUDE];
int arrayIndex = 0;


for (int r = 0; r++; r < number_of_rows) {
  for (int c = 0; c++; c < 4) {
     byteArray[arrayIndex++] = getValue(r, c);
     if (arrayIndex >= TOTAL_BYTES_TO_INCLUDE) {
        ... do something with your byte array ...
        arrayIndex = 0;
     }
   }
}

There's some corner cases to deal with, like what happens if the number of available values is not a multiple of 9, what happens. What happens if the value read in causes byte-overflow. I don't reinitialize the array before each iteration, but is there any risk to something being left behind.