Convert binary string to byte-Array in Java

Question

I have a binary string and I want to split it into chunks of length 8 and then store the corresponding bytes in a byte-Array. For example, the string "0000000011111111" should be convertert to {-128, 127}. So far, I wrote the following function:

public static byte[] splitBinary(String binaryString) throws ConversionException {

    if (binaryString.length()%8 != 0) {
        throw new ConversionException();
    }

    byte[] result = new byte[binaryString.length()/8];

    while (i < result.length) {
        result[i] = (byte) (Integer.parseInt(binaryString.substring(i, i+8), 2)-128);
        i+=8;
    }
    return result;
}

But this results in {-128, 0}. How can I achieve the desired functionality?

@SandeepKumar OP wrote should be convertert to {-128, 127} — Scary Wombat
– Scary Wombat, Commented Dec 16, 2019 at 8:28
Yes: the input is the string "0000000011111111" and the output shoud be the byte array {-128, 127}. — maria93
– maria93, Commented Dec 16, 2019 at 8:29
@Vihar No! That would result in accesing result[8] which is invalid. — Seelenvirtuose
– Seelenvirtuose, Commented Dec 16, 2019 at 8:31
@Seelenvirtuose a different index can be used for result, but according to the question this is the index the next iteration should take iteration 1 : 0 to 7 iteration 2 : 8 to 15 and so on — Vihar
– Vihar, Commented Dec 16, 2019 at 8:33

maria93 · Accepted Answer · 2019-12-16 09:11:09Z

I changed the function in the following way and now it works as expected (after correcting my expectations ;)). Thank you all!

public static byte[] splitBinaryStringToByteArray(String binaryString) throws ConversionException {

    if (binaryString.length()%8 != 0) {
        throw new ConversionException();
    }

    byte[] result = new byte[binaryString.length()/8];

    int i =0;int j=0;
    while (i < binaryString.length()) {
        System.out.println("Substring: " + binaryString.substring(i, i+8));
        result[j] =((byte)Integer.parseInt((binaryString.substring(i, i+8)), 2));
        j++;
        i+=8;
    }
    return result;
}

Nicktar · Accepted Answer · 2019-12-16 08:29:23Z

0

Your splitting routine is wrong.

increasing i by 1 just moves your window one charachter to the right, not two, resulting in die Strings 00000000 and 00000001 to be read.

answered Dec 16, 2019 at 8:29

Nicktar

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3 Comments

maria93 Over a year ago

Thank you! I changed it in the question. But now it leads to {-128,0}.

Nicktar Over a year ago

You change your question and the downvote an answer for no longer fitting your changed question?

maria93 Over a year ago

I did not downvote anyone! I just wanted to use your helpful comment...

milanbalazs · Accepted Answer · 2019-12-16 09:36:47Z

0

I refer to result's size, it may smaller than size of binaryString, but in binaryString.substring(i, i+8) and i+=8; you use as size of binaryString. So change them to binaryString.substring(i*8, i*8+8) and i++.

edited Dec 16, 2019 at 9:36

milanbalazs

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answered Dec 16, 2019 at 8:48

sunsunsun

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