Re: Execution jvm commands from java

From:
Patricia Shanahan <pats@acm.org>
Newsgroups:
comp.lang.java.programmer
Date:
Mon, 31 Jul 2006 15:35:48 GMT
Message-ID:
<orpzg.6194$gF6.159@newsread2.news.pas.earthlink.net>
Patricia Shanahan wrote:

Oliver Wong wrote:

"shaposhnik" <yaron.shaposhnik@gmail.com> wrote in message
news:1154354039.727701.129240@i3g2000cwc.googlegroups.com...

i am trying to implement a state machine.
currently it is working as a while loop with a switch and many cases on
the state number, and a break after every case. i was hoping to speed
it up by using goto's.


   Do you realize that switch, break, and while loops all compile to
goto and conditional jump statements at the bytecode level anyway?

   - Oliver


However, you don't need the equivalent of switch, at least in the same
sense, to implement a goto-based state machine. The code for a single
state looks something like:

state_20:
   do something;
   if(some condition)
      goto state_30;
   else
      goto state_21;


A State interface would probably be the most similar Java approach to this:

interface State{
   State nextState([some parameters]);
}

with lots of references to subclass instances:

State someStateName = new State(){
   State nextState([some parameters]){
     do something;
     if(some condition)
       return someOtherState;
     else
       return yetAnotherState;
   }
};

With a driving loop of the form:

State state = startState;
while(state != endState){
   state = state.nextState(some parameters);
}

However, for a large monolithic state machine, this would end up with
hundreds of anonymous inner class files, one for each state.

Patricia

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