How to convert array of 16-bit signed integers to byte array in Java?

Question

Let's say that on Android (Java) we have a byte array that represents a sequence of 16-bit signed integers.

I am needing to be able to decode the values from this array by using a for-loop and concatenating each pair of bytes to retrieve the original value back again (Please don't suggest a different method such as a ByteBuffer).

In order to test my algorithm, I want to encode and decode a list of ints and see if I get the same numbers back.

However, I can't figure out how to encode the original list of ints into a byte array for testing purposes. I don't want to simply reverse my algorithm because I don't know if it works yet... I would be open to using ByteBuffer or any other known-good means to do the encoding because it's only for testing/simulation purposes -- in the real app, the byte array is already encoded by Android.AudioRecord.

    // dec : short : byte a : byte b
    // 4536 : 0001000100000100 : 17 : 4
    // -1 : 1111111111111111 : -1 : -1
    // -32768 : 1000000000000000 : -128 : 0 
    // 32767 : 1000000000000001 : -128 : 1
    // 0 : 0000000000000000 : 0 : 0
    // -2222 : 1111011101010010 : -9 : 82

void _go() {
        
        int[] source = {4536,-1,-32768,32767,0,-2222};

        // is this even correct?
        byte[] expectedEncoding = {17,4,-1,-1,-128,0,-128,1,0,0,-9,82};

        byte[] encoded = ??? // <----- what goes here?

        int[] decoded = new int[source.length];

        // the algorithm I'm testing
        for (int i=0; i < encoded.length/2; i++) {
            byte a = encoded[i];
            byte b = encoded[i+1];

            decoded[i] = (short) (a<<8 | b & 0xFF);

        }

        Log.i("XXX", "decoded values: " + decoded.toString());
        
    }

what about splitting each int into four parts (i&0xFF, (i>>8)&0xFF, (i>>16)&0xFF and (i>>24)&0xFF)? — dan1st
– dan1st, Commented Jan 21, 2023 at 23:03
Note that an int in Java is a 32-bit signed integer. Or are you saying only the low 16-bits are ever used? — Slaw
– Slaw, Commented Jan 22, 2023 at 1:36

Robert · Accepted Answer · 2023-01-22 13:11:51Z

1

Here an exemple...

short[] arrayOfShorts = {6, 1, 2, 5};
byte[] arrayOfBytes = new byte[shortArray.length * 2];
ByteBuffer.wrap(byteArray)
                 .order(ByteOrder.LITTLE_ENDIAN)
                 .asShortBuffer().put(shortArray);

edited Jan 22, 2023 at 13:11

answered Jan 21, 2023 at 23:03

Robert

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