monq.jfa.actions

Class SwitchDfa

java.lang.Object

monq.jfa.AbstractFaAction

monq.jfa.actions.SwitchDfa

All Implemented Interfaces:

java.io.Serializable, FaAction

public class SwitchDfa
extends AbstractFaAction

implements an FaAction which changes the Dfa operated by the calling DfaRun. This type of action is useful whenever different parts of the input shall be handled by different Dfas.

In a typical example, the input contains long stretches of irrelevant text interspersed by parts which need closer examination. Given that start and end of the relevant parts can be detected by regular expressions rIn and rOut, two Dfas can be set up like this:

   SwitchDfa toWork = new SwitchDfa(Drop.DROP);
   SwitchDfa toSkip = new SwitchDfa(Drop.DROP);
   Dfa skip = new Nfa(rIn, toWork)
                  .or(  other stuff )
                  .compile(DfaRun.UNMATCHED_DROP);
   Dfa work = new Nfa(rOut, toSkip)
                  .or(  other stuff )
                  .compile(DfaRun.UNMATCHED_COPY);
   // don't forget to set up the switches.
   toWork.setDfa(work);
   toSkip.setDfa(skip);
   DfaRun r = new DfaRun(skip, ...);

When rIn is detected, toWork.invoke() gets called which switches the calling DfaRun to run the automaton work. When later the end of the relevant part is detected by a match with rOut, the a call to toSkip.invoke() switches back to automaton skip. Because of the mutual reference between the automata and objects of this class, the constructor does not take a Dfa as an argument. Rather setDfa() must be used.

Version:

$Revision: 1.8 $, $Date: 2005-09-19 14:01:58 $

Author:

© 2003, 2004 Harald Kirsch

See Also:

Serialized Form

Constructor Summary

Constructors

Constructor and Description
SwitchDfa() calls the 1 parameter constructor with action==null.
SwitchDfa(FaAction action) creates an FaAction to switch the calling DfaRun object to another Dfa.

Method Summary

Modifier and Type	Method and Description
void	invoke(java.lang.StringBuilder out, int start, DfaRun r) is called by methods of DfaRun in case of a match.
void	setDfa(Dfa dfa) sets the Dfa this action switches the calling DfaRun to.

Methods inherited from class monq.jfa.AbstractFaAction

mergeWith, setPriority

Methods inherited from class java.lang.Object

equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

SwitchDfa

public SwitchDfa(FaAction action)

creates an FaAction to switch the calling DfaRun object to another Dfa. The Dfa must be set later with setDfa(). The parameters influence the operation of the invoke() callback as follows:

1. The Dfa, which you have to specify by calling setDfa(monq.jfa.Dfa), will be entered into the calling DfaRun.
2. If action is not null, the action will then be invoked. Without action, the triggering text will show up in the output. To drop it, set action to Copy.COPY.

SwitchDfa

public SwitchDfa()

calls the 1 parameter constructor with action==null.

Method Detail

setDfa

public void setDfa(Dfa dfa)

sets the Dfa this action switches the calling DfaRun to. This function must be called once before the action is used.

invoke

public void invoke(java.lang.StringBuilder out,
                   int start,
                   DfaRun r)
            throws CallbackException

Description copied from interface: FaAction

is called by methods of DfaRun in case of a match. Parameter yytext contains the matching text from position start onwards. The callback may change the whole of yytext, but the under most circumstances, only the matching text should be changed. Parameter runner is the DfaRun object which called this function. Of interest are its fields DfaRun.clientData and DfaRun.collect.

Throws:

CallbackException