Question

i have a question for call management.

I get a message with a payload of 3 bytes in a byte[]. Different bits in there leads to calling another method. I did it with a logical AND between the byte and a shiftet 1 to get the value of the bit. I used if elseif etc. to call the specific method. Is there another possibilty to realise it, maybe a HashMap or something?

At least im forced to use max. Java 1.4

Greetings,
fnobbi

Answer 1

It depends on how many different methods you are calling. If it’s less than (I’m guessing here) 20, I would use simple bit-mask tests on a int (which is 4 bytes – use the lower 3) with if().

For example:

public static void callMethod(byte[] bytes) {
    int bits = (bytes[2] & 0xFF) << 16 +
               (bytes[1] & 0xFF) << 8 + 
               (bytes[0] & 0xFF);
    if ((bits & 1) > 0) {
        methodForBit0Set(bytes);
    }
    if ((bits & 2) > 0) {
        methodForBit1Set(bytes);
    }
    if ((bits & 4) > 0) {
        methodForBit3Set(bytes);
    }
    // etc
}

If you’re only calling one method then stopping, you’ll want to use elses between the ifs, and may also want to order the tests in order of most-frequently expected first.

Using a hashmap wouldn’t be that much faster than these extremely fast operations IMHO even if you have lots of tests, and this is easier to read, debug and maintain.