equivalent of memcmp() in Java?

Memcmp returns an int, less than, equal to, or greater than zero if the first n bytes of s1 is found, respectively, to be less than, to match, or be greater than the first n bytes of s2. Equals returns a boolean. It's not the same function. In addition, memcmp compares bytes as unsigned chars.

I think this could work:

public int memcmp(byte b1[], byte b2[], int sz){
    for(int i = 0; i < sz; i++){
        if(b1[i] != b2[i]){
            if(b1[i] >= 0 && b2[i] >= 0)
                return b1[i] - b2[i];
            if(b1[i] < 0 && b2[i] >= 0)
                return 1;
            if(b2[i] < 0 && b1[i] >= 0)
                return -1;
            if(b1[i] < 0 && b2[i] < 0){
                byte x1 = (byte) (256 + b1[i]);
                byte x2 = (byte) (256 + b2[i]);
                return x1 - x2;
            }
        }
    }
    return 0;
}

(edit) In fact, the 2's complement part is not necessary:

public static int memcmp(byte b1[], byte b2[], int sz){
    for(int i = 0; i < sz; i++){
        if(b1[i] != b2[i]){
            if((b1[i] >= 0 && b2[i] >= 0)||(b1[i] < 0 && b2[i] < 0))
                return b1[i] - b2[i];
            if(b1[i] < 0 && b2[i] >= 0)
                return 1;
            if(b2[i] < 0 && b1[i] >=0)
                return -1;
        }
    }
    return 0;
}

There's Arrays.equals().

I don't know whether the JVM implementation actually optimizes this if a corresponding instruction exists in the hardware, but I doubt it.

Also, if I remember my C correctly, strcmp works up to a null terminator (making it useful for C strings), The Arrays version will compare the entire array since Java programmers rarely bother with null-terminated arrays. You could easily write your own function, though, if you care about the null-terminator.

The java.util.Arrays.equals(byte[], byte[]) method is your friend.