通过添加 256 将字节数组中的负字节变为正字节 - java

Question

I have a byte array:

byte[] b = [108, 108, -17, 65] // Arrays.toString(b)

and I want to turn negatives into negatives +256, like: -17 + 256 = 239 so that I have:

b = [108, 108, 239, 65]

I tried:

ByteBuffer buffer = ByteBuffer.wrap(b);

for(int i = 0; i < 4; i++){
   if (b[i] < 0){
      int n = (b[i] + 256);
      byte b1 = (byte) (b[i] + 256);

      buffer.position(i);
      buffer.put(i, (byte) (n & 0xFF));
   }
}

but nothing changes. I would be very thankful for any advices

Answer 1

You can't represent anything over 127 as a positive valued byte. So you would have to have an array of ints to show the value like you want. I use the word show because it is important to realize that this is just a representation of the actual value for use by humans. It has no bearing on the intrinsic nature of the value.

byte b = 239;
System.out.println(b);

Prints

-17

I suspect you would want the unsigned value which can be printed like so.

byte b = -17;
System.out.println(Byte.toUnsignedInt(b));

Prints

239