monq.jfa

Class AbstractFaAction

java.lang.Object

monq.jfa.AbstractFaAction

All Implemented Interfaces:

java.io.Serializable, FaAction

Direct Known Subclasses:

Call, Context, Copy, Count, Drop, Embed, Fail, Hold, If, IfContext, LowerCase, Printf, Replace, Run, SearchReplace, Stop, Store, SwitchDfa, TailContextN, UpperCase

public abstract class AbstractFaAction
extends java.lang.Object
implements java.io.Serializable, FaAction

implements the prototype of an FaAction with initial priority zero so that actions can be easily written as anonymous classes. For a bunch of useful actions have a look at the subpackage monq.jfa.actions.

Author:

© 2003, 2004 Harald Kirsch

See Also:

Serialized Form

Constructor Summary

Constructors

Constructor and Description
AbstractFaAction() although this class is abstract, the constructor is needed to create anonymous subclasses.

Method Summary

Modifier and Type	Method and Description
FaAction	mergeWith(FaAction _other) is eventually called by Nfa.compile(monq.jfa.DfaRun.FailedMatchBehaviour, monq.jfa.FaAction) to create a unified action from this object and another FaAction object.
AbstractFaAction	setPriority(int p)

Methods inherited from class java.lang.Object

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

Methods inherited from interface monq.jfa.FaAction

invoke

Constructor Detail

AbstractFaAction

public AbstractFaAction()

although this class is abstract, the constructor is needed to create anonymous subclasses.

Method Detail

setPriority

public AbstractFaAction setPriority(int p)

mergeWith

public FaAction mergeWith(FaAction _other)

Description copied from interface: FaAction

is eventually called by Nfa.compile(monq.jfa.DfaRun.FailedMatchBehaviour, monq.jfa.FaAction) to create a unified action from this object and another FaAction object. During compilation of an Nfa into a Dfa, two regular expressions assigned to different actions may have overlapping matches. In this case one of the actions' mergeWith methods is called with the other action as parameter to create a unified action object.

There are only four permissible results this method may return:

1. this completely unchanged,
2. other completely unchanged,
3. a newly created object or
4. null to signal that no unified action exists.

Both objects, this and other must be treated read-only. Changing them may lead to unexpected behaviour which is very hard to track down. To understand why this is so, consider the two regular expressions ax? and ay? bound to actions X and Y respectively. Both expressions match the string "a", which will cause a call to mergeWith of either one of the actions. If merging would integrate, say, Y into X and return X, the changed X would also be run for the match "ax" which most likely was not intended.

To get a simple priority based selection of one of the actions, consider extending AbstractFaAction.

Note: For two competing actions it is completely random which of the mergeWith() methods is called. Consequently, implementations of this method should be as symmetric as possible.

Specified by:

mergeWith in interface FaAction

Parameters:

_other - will never be null.