org.eclipse.emf.query.handlers
Class PruneHandler
java.lang.Object
org.eclipse.emf.query.handlers.PruneHandler
-
public abstract class PruneHandler
- extends
Object
An abstract class that represents a prune handler. It is used by EObjectConditions
to check if a given EObject has children -recursively- that are worth evaluating,
or, if all the contained EObjects for the given EObject will never satisfy the
EObjectCondition at all, and hence there is no need to check them at all.
It is important for clients to know that
pruning is treated as a hint only and is used solely to improve query performance
and should not be relied on for correctness of the EObjectCondition evaluation.
An EObjectCondition could not be consulted at all on pruning issue, and, its
response -if it get consulted- might not be honoured by the query -especially
when having an EObjectCondition logically combined with another.
Clearly this PruneHandler is an EObjectCondition and a metamodel specific, and that's
why there is no default implementation other than the trivial cases of prune-always
or never-prune. EObjectCondition that use a PruneHandler usually default to using
the PruneHandler.NEVER so as to visit and evaluate every child in the EObject containment tree,
in this sense, providing a PruneHandler by clients is optional, nevertheless, it is
there to allow clients to provide their own implementation as a way to enhance
performance of queries by not visiting useless branches.
This class is intended to be subclassed by clients.
|
Field Summary
|
static
PruneHandler
|
ALWAYS
A simple PruneHandler implementation that will always prune
regardless of the nature of the EObjectCondition used or the argument
eObject passed. |
static
PruneHandler
|
NEVER
A simple PruneHandler implementation that will never prune
regardless of the nature of the EObjectCondition used or the argument
eObject passed. |
|
Method Summary
|
abstract boolean
|
shouldPrune
(
EObject eObject)
Answers whether the children -recursively- of the argument EObject are
not worth evaluating by a given EObjectCondition
|
|
Methods inherited from class java.lang.
Object
|
clone,
equals,
finalize,
getClass,
hashCode,
notify,
notifyAll,
toString,
wait,
wait,
wait
|
ALWAYS
public static final
PruneHandler ALWAYS
- A simple
PruneHandler implementation that will always prune
regardless of the nature of the EObjectCondition used or the argument
eObject passed. The shouldPrune(EObject) will always return true.
NEVER
public static final
PruneHandler NEVER
- A simple
PruneHandler implementation that will never prune
regardless of the nature of the EObjectCondition used or the argument
eObject passed. The shouldPrune(EObject) will always return false.
PruneHandler
public PruneHandler()
shouldPrune
public abstract boolean shouldPrune(
EObject eObject)
- Answers whether the children -recursively- of the argument
EObject are
not worth evaluating by a given EObjectCondition
-
-
Parameters:
-
eObject - The EObject whose children are being checked.
-
Returns:
- boolean
true if this prune handler finds out that the argument
eObject's children -recursively- will always evaluate to false by the
respective EObjectCondition that this PruneHandler is written to help.
