Class SucceedsOncePredicate

java.lang.Object

org.projog.core.predicate.SucceedsOncePredicate

All Implemented Interfaces:

Predicate

public class SucceedsOncePredicate
extends Object
implements Predicate

Field Summary

Fields

Modifier and Type	Field	Description
static final SucceedsOncePredicate	SINGLETON

Method Summary

Modifier and Type	Method	Description
boolean	couldReevaluationSucceed()	Could the next re-evaluation of this instance succeed?
boolean	evaluate()	Attempts to satisfy the goal this instance represents.

Methods inherited from class Object

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

Field Details

SINGLETON

public static final SucceedsOncePredicate SINGLETON

Method Details

evaluate

public boolean evaluate()

Description copied from interface: Predicate

Attempts to satisfy the goal this instance represents.

Calling this method multiple times on a single instance allows all possible answers to be identified. An attempt to find a solution carries on from where the last successful call finished.

If PredicateFactory.isRetryable() returns false then this method should only be called once per individual query (no attempt should be made to find alternative solutions).

If PredicateFactory.isRetryable() returns true then, in order to find all possible solutions for an individual query, this method should be recalled on backtracking until it returns false.

Specified by:

evaluate in interface Predicate

Returns:

true if it was possible to satisfy the clause, false otherwise

See Also:

• PredicateFactory.getPredicate(Term)

couldReevaluationSucceed

public boolean couldReevaluationSucceed()

Description copied from interface: Predicate

Could the next re-evaluation of this instance succeed?

Specifies whether a specific instance of a specific implementation of Predicate, that has already had Predicate.evaluate() called on it at least once, could possibly return true the next time Predicate.evaluate() is called on it. i.e. is it worth trying to continue to find solutions for the specific query this particular instance represents and has been evaluating?

(Note: the difference between this method and PredicateFactory.isRetryable() is that PredicateFactory.isRetryable() deals with whether, in general, a specific implementation (rather than instance) of Predicate could ever produce multiple answers for an individual query.)

Specified by:

couldReevaluationSucceed in interface Predicate

Returns:

true if an attempt to re-evaluate this instance could possible succeed, false otherwise