Re: finite state machine with enum

andijcr <>
Wed, 10 Feb 2010 15:00:21 -0800 (PST)
On 10 Feb, 20:02, Tom Anderson <> wrote:

On Wed, 10 Feb 2010, andijcr wrote:

i have a byte stream that has to be decoded in a list of simple
containers - basically I do a translation from serial to parallel. The
implementation I'm using now has this form:

public class RawProtocol{

   private long millis=/*some initialization procedure*/;
   public RawProtocol(InputStream inputStream, OutputStream
outputStream){ LinkedBlockingQueue<Byte>();;

   public RawData getRawData() {
       Byte temp;
               return null;
         return a deserialized packet
        ... */

   enum Mlsm{ //stands for my little state machine

       START {
           public Mlsm exec(byte time){
               pushTime(time); //this byte represent=

s a time and

should be treated in a way
               return TIME_RED;
       TIME_RED {
           public Mlsm exec(byte value){
               pushValue(value); //this is a value a=

nd should be

treated in another way
               return VALUE_RED;
       VALUE_RED {
           public Mlsm exec(byte stop){
               switch (stop){
               case stopByte:
                   commit(); //the sequence (tim=

e - value) is well

formed and can be saved in a packet
                   return START;
               default: return GARBAGE;
       GARBAGE {
           public Mlsm exec(byte grbg){
               switch (grbg){
               case stopByte: return START;
               default: return this;

       public abstract Mlsm exec(byte b);

the machine is activated through getRawData, which makes it perform a
complete cycle to produce a single packet of formatted data

the initial idea to use a state machine implemented as an inner class
was to:
- bring order in the code

Seriously? You think that's more ordered than:

DataInputStream in;
while (true) {
        byte stop = in.readByte();
        if (stop == stopByte) {
        else {
                while ((stop = in.readByte()) != stop=





If what you've posted is really what you're doing, and not a huge
simplification of what you're actually doing, then you've massively
overcomplicated this.

- to take advantage of some time-dependent data (millis) managed by the
outer class RawProtocol (most important)

I don't see why you couldn't do that with the above loop.


It's rare that you're simply presented with a knob whose only two
positions are "Make History" and "Flee Your Glorious Destiny." --
Tycho Brahae

the snippet is a simplification of the real code, tough it is not so
much more complicated. Here i made the decision to use a simple
implementation of a state machine, instead of a sequence of methods,
for the elasticity i can obtain in the interpretation of the not-so-
stable underlying protocol.

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