Class Selectables

java.lang.Object

org.microbean.assign.Selectables

public final class Selectables
extends Object

Utility methods for working with Selectables.

Author:

Laird Nelson

See Also:

• Selectable

Method Summary

Modifier and Type	Method	Description
static <C,E> Selectable<C,E>	caching(Selectable<C,E> selectable)	Returns a Selectable that caches its results.
static <C,E> Selectable<C,E>	caching(Selectable<C,E> selectable, BiFunction<? super C, Function<? super C, ? extends List<E>>, ? extends List<E>> f)	Returns a Selectable that caches its results.
static final <C,E> Selectable<C,E>	empty()	Returns a Selectable whose Selectable.select(Object) method always returns an empty, immutable List.
static <C,E> Selectable<C,E>	filtering(Collection<? extends E> collection, BiPredicate<? super E, ? super C> p)	Returns a Selectable using the supplied Collection as its elements, and the supplied BiPredicate as its selector.

Methods inherited from class java.lang.Object

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

Method Details

caching

public static <C,E> Selectable<C,E> caching(Selectable<C,E> selectable)

Returns a Selectable that caches its results.

The cache is unbounded.

Type Parameters:

C - the criteria type

E - the element type

Parameters:

selectable - a Selectable; must not be null

Returns:

a non-null Selectable

Throws:

NullPointerException - if selectable is null

See Also:

• caching(Selectable, BiFunction)

caching

public static <C,E> Selectable<C,E> caching(Selectable<C,E> selectable,
 BiFunction<? super C, Function<? super C, ? extends List<E>>, ? extends List<E>> f)

Returns a Selectable that caches its results.

Type Parameters:

C - the criteria type

E - the element type

Parameters:

selectable - a Selectable; must not be null

f - a BiFunction that returns a cached result, computing it on demand via its supplied mapping Function if necessary; must not be null; normally safe for concurrent use by multiple threads; often a reference to the ConcurrentHashMap.computeIfAbsent(Object, Function) method

Returns:

a non-null Selectable

Throws:

NullPointerException - if selectable or f is null

See Also:

• ConcurrentHashMap.computeIfAbsent(Object, Function)

empty

public static final <C,E> Selectable<C,E> empty()

Returns a Selectable whose Selectable.select(Object) method always returns an empty, immutable List.

This method is useful primarily for completeness and for testing pathological situations.

Type Parameters:

C - the criteria type

E - the element type

Returns:

a non-null Selectable

filtering

public static <C,E> Selectable<C,E> filtering(Collection<? extends E> collection,
 BiPredicate<? super E, ? super C> p)

Returns a Selectable using the supplied Collection as its elements, and the supplied BiPredicate as its selector.

There is no guarantee that this method will return new Selectable instances.

The Selectable instances returned by this method may or may not cache their selections.

The selector must (indirectly) designate a sublist from the supplied Collection as mediated by the supplied criteria. The selector must additionally be idempotent and must produce a determinate value when given the same arguments.

No validation of these semantics of the selector is performed.

Type Parameters:

C - the criteria type

E - the element type

Parameters:

collection - a Collection of elements from which sublists may be selected; must not be null

p - the selector; must not be null

Returns:

a Selectable; never null

Throws:

NullPointerException - if either collection or p is null