byte to int conversion & vice versa java

Question

I am trying to convert a integer into byte and retrieving the integer back in my code.

code:

ByteArrayOutputStream barrayStream = null;
        DataOutputStream outputStream = null;
        try {
            initSequence();
            barrayStream = new ByteArrayOutputStream();
            outputStream = new DataOutputStream(barrayStream);
            outputStream.writeByte(4);
            outputStream.writeInt(xxxx);
            System.out.println("  String = "
                    + Arrays.toString(barrayStream.toByteArray()));
            handlePacket(barrayStream.toByteArray());
        }catch (IOException ie) {


ie.printStackTrace();
        } finally {
            try {
                if (barrayStream != null) {
                    barrayStream.close();
                }
                if (outputStream != null) {
                    outputStream.close();
                }
            } catch (IOException e) {
                e.printStackTrace();
            }

void handlePacket(byte[] byteArray) throws IOException {

byte[] portArray = new byte[4];
System.arraycopy(byteArray, 1, portArray, 0, 4);
int byteToIntValue = 0;
        for (int i = 0; i < portArray.length; i++) {
            byteToIntValue = (byteToIntValue << 8) | portArray[i];
        }

        System.out.println("Port Number = " + byteToIntValue);
}

integer greater than 5120 gives the correct value while retrieving. But below 5119 gives the negative value Is there any specific reason for this. Any help will be appreciated.

output: for integer 5100 the output is [0, 0, 19, -20]

for integer greater than 5120 [0, 0, 20, 0]

Answer 1

Try this:

Byte to int:

Byte b = new Byte(rno[0]);
int i = b.intValue();

int to byte:

int i = 234;
byte b = (byte) i;

A byte is always signed in Java. You may get its unsigned value by binary-anding it with 0xFF, though:

Answer 2

This is happening because a Java byte is a signed value, between -128 and 127. You're parsing the port number correctly. It's just when you use Arrays.toString that the bytes get displayed as signed numbers.