Why are Byte.compare() and Integer.compare() implemented differently?

Question

I am studying the source of the OpenJDK.

My attention was attracted by the methods Byte.compare() and Integer.compare():

public static int Byte.compare(byte x, byte y) {
    return x-y;
}

public static int Integer.compare(int x, int y) {
    return (x < y) ? -1 : ((x == y) ? 0 : 1);
}

Why do the methods Byte.compare() and Integer.compare() have different implementations?

Answer 1

The implementation of Integer.compare does not use subtraction, as this could cause an overflow in case you're comparing an integer that is close to Integer.MIN_VALUE with another that is close to Integer.MAX_VALUE.

This overflow cannot happen in case of Byte.compare, as there the byte values are implicitely converted to integers before x-y is calculated.

(see also: Java Language Specification - 5.6.2 Binary Numeric Promotion)

Answer 2

The Byte method can be implemented this way, becasue the result of the subtraction is representable in int. This is not so in the other case. For example:

0 - 0x80000000 == 0x80000000

and this is negative, hence the comparision would wrongly indicate that 0 is smaller than -2^31