Re: finite state machine with enum
On 10 Feb, 20:02, Tom Anderson <t...@urchin.earth.li> 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){
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 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) {
pushTime(in.readByte());
pushValue(in.readByte());
byte stop = in.readByte();
if (stop == stopByte) {
commit();
}
else {
while ((stop = in.readByte()) != stop=
Byte);
}
}
?
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
--
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.