monq.jfa.ctx

Class IfContext

java.lang.Object

monq.jfa.AbstractFaAction

monq.jfa.ctx.IfContext

All Implemented Interfaces:

java.io.Serializable, FaAction

public class IfContext
extends AbstractFaAction

is an FaAction to execute different client actions depending on the Context in which IfContext.invoke() is called. Typical usage:

 nfa.or("regex", new IfContext(ctx1, action1)
                      .ifthen(ctx2, action2)
                      .ifthen(ctx3, action3)
                      .elsedo(actionDefault))

The context objects ctx1 etc. must be acquired before by use of a ContextManager.

It is not necessary to add all valid contexts for a certain "regex" with the same IfAction object. Any number of IfAction objects may be bound to the regular expression or to regular expressions which share matches. When the Nfa is compiled into a Dfa, mergeWith() will combine all actions into one.

See Also:

Serialized Form

Constructor Summary

Constructors

Constructor and Description
IfContext() create an action which does only perform default actions.
IfContext(Context ctx, FaAction a) creates an FaAction to run the given client action if called in the given Context.

Method Summary

Modifier and Type	Method and Description
IfContext	elsedo(FaAction a) define the action to call when this object's invoke method is called in a context for which no client action is registered.
IfContext	ifthen(Context ctx, FaAction a) defines to call the given action when this object's invoke method is called in the given context.
void	invoke(java.lang.StringBuilder yytext, int start, DfaRun r) required by interface FaAction.
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.
java.lang.String	toString()

Methods inherited from class monq.jfa.AbstractFaAction

setPriority

Methods inherited from class java.lang.Object

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

Constructor Detail

IfContext

public IfContext()

create an action which does only perform default actions.

IfContext

public IfContext(Context ctx,
                 FaAction a)

creates an FaAction to run the given client action if called in the given Context.

See Also:

ifthen(monq.jfa.ctx.Context, monq.jfa.FaAction)

Method Detail

ifthen

public IfContext ifthen(Context ctx,
                        FaAction a)

defines to call the given action when this object's invoke method is called in the given context.

NOTE: The given Context may be null to indicate that the action should be run if no context is (yet) on the stack.

elsedo

public IfContext elsedo(FaAction a)

define the action to call when this object's invoke method is called in a context for which no client action is registered. The default action used if this method is not called mimics the behaviour of the calling DfaRun for unmatched text.

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

Overrides:

mergeWith in class AbstractFaAction

Parameters:

_other - will never be null.

invoke

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

required by interface FaAction.

Throws:

CallbackException

toString

public java.lang.String toString()

Overrides:

toString in class java.lang.Object