Java ME中字节数组的字符

Question

Is this the correct way to bit shift into a char?

char value = (char)((array[offset] << 9) + (array[offset + 1]));

If not, please correct me.

Answer 1

Bytes in Java are a bit tricky. They don't go from 0 to 255 like you might be used to from other languages. Instead, they go from 0 to 127 and then from -128 to -1.

This means, that all bytes in your byte array that is below 128 will be converted into the correct char with this code:

char value = (char)((array[offset] << 8) + (array[offset + 1]));

But if the byte value is above 127, you'll probably get results you didn't expect.

Small example:

class test {

  public static void main(String[] args) {

    byte b = (byte)150;
    char c = (char)b;
    int i = (int)c;

    System.out.println(b);
    System.out.println(c);
    System.out.println(i);

  }
}

Will output this:

-106
ﾖ
65430

Not exactly what you might expect. (Depending of course how well you know Java).

So to properly convert 2 bytes into a char, you'd probably want a function like this:

char toChar(byte b1, byte b2) {
  char c1 = (char)b1;
  char c2 = (char)b2;
  if (c1<0) c1+=256;
  if (c2<0) c2+=256;
  return (char)((c1<<8)+c2);
}