monq.jfa

Class Dfa

java.lang.Object

monq.jfa.Dfa

All Implemented Interfaces:

java.io.Serializable

public class Dfa
extends java.lang.Object
implements java.io.Serializable

implements a deterministic finite automaton. In contrast to class Nfa, objects of this class do not allow operations which change the automaton structure. But only a Dfa can be operated by a DfaRun to filter text. This makes sure that the automaton structure is not changed while a DfaRun is working with it.

A Dfa can only be created by calling one of the Nfa.compile() methods. It can only be used for matching by operating it in a DfaRun object. To apply automata-operations again, it is necessary to copy it into a Nfa again with toNfa().

Warning: The intention of separating the data structure encapsulated in a Dfa from the machinery to run it, i.e. DfaRun, is that Dfa objects shall be shareable between threads. For this to work, however, make sure that each FaAction used in the Dfa has either no internal state or is synchronized. To pass data between actions, use DfaRun.clientData.

Author:

© 2003, 2004, 2005 Harald Kirsch

See Also:

Serialized Form

Field Summary

Fields

Modifier and Type	Field and Description
long	matchMax maximum length a match can have.

Method Summary

Modifier and Type	Method and Description
DfaRun	createRun() convenience function to get a DfaRun for this automaton.
FaAction	match(CharSource in, java.lang.StringBuilder out, TextStore subMatches) determine a matching prefix of in and deliver respective data.
boolean	matchesEmpty() returns true if this automaton can match the empty string.
void	toDot(java.io.PrintStream out) prints a graph representation of the Dfa in the graphviz format.
void	toDot(java.lang.String filename)
Nfa	toNfa() converts the Dfa back into an Nfa in a way that this is totally useless afterwards.

Methods inherited from class java.lang.Object

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

Field Detail

matchMax

public long matchMax

maximum length a match can have. If the value is greater zero, no match found by this object will be longer. If matchMax is left at its default -1, the longest match found will be no longer than 2⁶⁴ characters, which is probably long after you ran out of memory.

Method Detail

matchesEmpty

public boolean matchesEmpty()

returns true if this automaton can match the empty string. If this can match the empty string, it should better not be used with a DfaRun because many methods of DfaRun will be likely to enter an infinite loop.

createRun

public DfaRun createRun()

convenience function to get a DfaRun for this automaton.

toNfa

public Nfa toNfa()

converts the Dfa back into an Nfa in a way that this is totally useless afterwards. Make sure it is not used somewhere else meanwhile. The approach was taken for efficiency reasons. A deep copy operation is not implemented.

Returns:

an Nfa containing all Dfa nodes plus a common stop state required by the Nfa data structure.

toDot

public void toDot(java.io.PrintStream out)

prints a graph representation of the Dfa in the graphviz format.

toDot

public void toDot(java.lang.String filename)

match

public FaAction match(CharSource in,
                      java.lang.StringBuilder out,
                      TextStore subMatches)
               throws java.io.IOException

determine a matching prefix of in and deliver respective data. If in can be matched by the Dfa the matching text is appended to out and the associated action is returned. If subMatches is not null, the submatches, if any, are analyzed and provided in subMatches after first clearing it.

Parameters:

subMatches - may be null, if no submatch analysis is requested.

Returns:

either the action associated with the match found or null if no match was found.

Throws:

java.io.IOException