Get unsigned bytes in Java

Question

Is there any way to read bytes in Java and to have the same "format" result than in C#?

Indeed in Java, bytes are signed (-128, +127), where in C# it's not (0, 255).

I'm sending files with a java application to a server who is expecting only positive bytes, so it's not working as soon as I have some negative bytes.

Concrete problem : when I'm serializing my bytes[] into json (using gson), I have values from -128 to + 127 whereas I'd like to have value from 0 to 255.

Hope it's clear enough.

Thank you.

There is no such thing as a 'positive byte'. A byte is 8 bits. The difference is how you represent numbers with bytes. C# bytes are unsigned using plain ol' base 2 and java bytes are between -128 to 127 using 2's complement. 11111111 and 11111111 are the same byte both in C# and java. — Benjamin Gruenbaum
– Benjamin Gruenbaum, Commented Feb 6, 2013 at 23:54
Please tell more about the concrete problem for which you incorrectly thought that this is the solution. — BalusC
– BalusC, Commented Feb 6, 2013 at 23:55

nneonneo · Accepted Answer · 2013-02-06 23:55:50Z

12

If you want to get [0-255] values in the Java app, use a construct like (b & 0xff) to get a positive int from a byte.

answered Feb 6, 2013 at 23:55

nneonneo

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AdrianES · Accepted Answer · 2014-01-23 15:06:56Z

Java byte is signed from -128 to 127, if u want to get the representation from 0 to 255 i use this 2 functions

public static byte fromIntToByte(String value) throws Exception {
        return fromIntToByte(Integer.parseInt(value));
    }

    public static byte fromIntToByte(int value) throws Exception {
        String stringByte = "";
        if (value < 0 && value > 255) {
            throw new Exception("Must be from 0<=value<=255");
        }
        if (value <= 127) {
            for (int i = 0; i < 8; i++) {
                stringByte = String.valueOf(value % 2) + stringByte;
                value = value / 2;
            }
        } else {
            value = value / 2;
            for (int i = 0; i < 7; i++) {
                stringByte = String.valueOf(value % 2) + stringByte;
                value = value / 2;
            }
            stringByte = "-" + stringByte;
        }
        System.out.println(stringByte);
        byte b = Byte.parseByte(stringByte, 2);
        return b;
    }

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