Re: finite state machine with enum

From:
Tom Anderson <twic@urchin.earth.li>
Newsgroups:
comp.lang.java.programmer
Date:
Wed, 10 Feb 2010 19:02:55 +0000
Message-ID:
<alpine.DEB.1.10.1002101850380.10085@urchin.earth.li>
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){
       this.bq=new LinkedBlockingQueue<Byte>();
       this.is=inputStream;
       this.os=outputStream;
   }

   public RawData getRawData() {
       Byte temp;
       do{
           if((temp=bq.poll())!=null)
           state=state.exec(temp);
           else
               return null;
       }while(state!=Mlsm.START);
       /*...
         return a deserialized packet
        ... */
   }

   enum Mlsm{ //stands for my little state machine

       START {
           public Mlsm exec(byte time){
               pushTime(time); //this byte represents 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 and should be
treated in another way
               return VALUE_RED;
           }
       },
       VALUE_RED {
           public Mlsm exec(byte stop){
               switch (stop){
               case stopByte:
                   commit(); //the sequence (time - 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) {
  pushTime(in.readByte());
  pushValue(in.readByte());
  byte stop = in.readByte();
  if (stop == stopByte) {
  commit();
  }
  else {
  while ((stop = in.readByte()) != stopByte);
  }
}

?

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.

tom

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