Interface Reducible<C,T>

Type Parameters:

C - the type of criteria

T - the element type

All Known Implementing Classes:

Beans

Functional Interface:

This is a functional interface and can therefore be used as the assignment target for a lambda expression or method reference.

@FunctionalInterface
public interface Reducible<C,T>

A functional interface whose implementations can reduce an unspecified notional collection of elements to a single element according to some criteria.

This interface is related to, but should not be confused with, the Reducer interface, implementations of which can be used to build Reducible instances.

Author:

Laird Nelson

See Also:

• reduce(Object)
• Reducer

Method Summary

Modifier and Type	Method	Description
static <C, E> Reducible<C,E>	of(Selectable<C,E> selectable, Reducer<C,E> r)	Calls the of(Selectable, Reducer, BiFunction) method with the supplied selectable, the supplied r, and a reference to the Reducer.fail(List, Object) method, and returns the result.
static <C, E> Reducible<C,E>	of(Selectable<C,E> selectable, Reducer<C,E> r, BiFunction<? super List<? extends E>,? super C,? extends E> failureHandler)	Returns a Reducible implementation that uses the supplied Reducer for its reduction operations.
static <C, E> Reducible<C,E>	ofCaching(Selectable<C,E> selectable, Reducer<C,E> r)	Calls the ofCaching(Selectable, Reducer, BiFunction) method with the supplied selectable, the supplied r, the supplied failureHandler, and a reference to the Reducer.fail(List, Object) method, and returns its result.
static <C, E> Reducible<C,E>	ofCaching(Selectable<C,E> selectable, Reducer<C,E> r, BiFunction<? super List<? extends E>,? super C,? extends E> fh)	Calls the ofCaching(Selectable, Reducer, BiFunction, BiFunction) method with the supplied selectable, the supplied r, the supplied fh, and a reference to the computeIfAbsent(Object, Function) method of a new ConcurrentHashMap, and returns its result.
static <C, E> Reducible<C,E>	ofCaching(Selectable<C,E> selectable, Reducer<C,E> r, BiFunction<? super List<? extends E>,? super C,? extends E> fh, BiFunction<? super C,Function<C,E>,? extends E> cache)	Returns a Reducible implementation that uses the supplied Reducer for its reduction operations and the supplied computeIfAbsent BiFunction for its caching implementation.
T	reduce(C criteria)	Given a criteria object, which may be null, returns an object that represents the reduction of a notional collection of objects.

Method Details

reduce

T reduce(C criteria)

Given a criteria object, which may be null, returns an object that represents the reduction of a notional collection of objects.

Most Reducible implementations will return determinate values from invocations of this method, but there is no requirement to do so.

Parameters:

criteria - the criteria; may be null to indicate no criteria

Returns:

a single object, or null

Throws:

ReductionException - if reduction could not occur or if an error occurs

of

static <C,
E> Reducible<C,E> of(Selectable<C,E> selectable,
 Reducer<C,E> r)

Calls the of(Selectable, Reducer, BiFunction) method with the supplied selectable, the supplied r, and a reference to the Reducer.fail(List, Object) method, and returns the result.

Type Parameters:

C - the criteria type

E - the element type

Parameters:

selectable - a Selectable; must not be null

r - a Reducer; must not be null

Returns:

a Reducible; never null

Throws:

NullPointerException - if selectable or r is null

See Also:

• of(Selectable, Reducer, BiFunction)
• Reducer.fail(List, Object)

of

static <C,
E> Reducible<C,E> of(Selectable<C,E> selectable,
 Reducer<C,E> r,
 BiFunction<? super List<? extends E>,? super C,? extends E> failureHandler)

Returns a Reducible implementation that uses the supplied Reducer for its reduction operations.

Type Parameters:

C - the criteria type

E - the element type

Parameters:

selectable - a Selectable; must not be null

r - a Reducer; must not be null

failureHandler - a BiFunction serving as the supplied Reducer's failure handler; must not be null

Returns:

a Reducible; never null

Throws:

NullPointerException - if any argument is null

See Also:

• Reducer

ofCaching

static <C,
E> Reducible<C,E> ofCaching(Selectable<C,E> selectable,
 Reducer<C,E> r)

Calls the ofCaching(Selectable, Reducer, BiFunction) method with the supplied selectable, the supplied r, the supplied failureHandler, and a reference to the Reducer.fail(List, Object) method, and returns its result.

Type Parameters:

C - the criteria type

E - the element type

Parameters:

selectable - a Selectable; must not be null

r - a Reducer; must not be null

Returns:

a Reducible; never null

Throws:

NullPointerException - if any argument is null

See Also:

• ofCaching(Selectable, Reducer, BiFunction)

ofCaching

static <C,
E> Reducible<C,E> ofCaching(Selectable<C,E> selectable,
 Reducer<C,E> r,
 BiFunction<? super List<? extends E>,? super C,? extends E> fh)

Calls the ofCaching(Selectable, Reducer, BiFunction, BiFunction) method with the supplied selectable, the supplied r, the supplied fh, and a reference to the computeIfAbsent(Object, Function) method of a new ConcurrentHashMap, and returns its result.

Type Parameters:

C - the criteria type

E - the element type

Parameters:

selectable - a Selectable; must not be null

r - a Reducer; must not be null

fh - a BiFunction serving as the supplied Reducer's failure handler; must not be null

Returns:

a Reducible; never null

Throws:

NullPointerException - if any argument is null

See Also:

• ofCaching(Selectable, Reducer, BiFunction, BiFunction)

ofCaching

static <C,
E> Reducible<C,E> ofCaching(Selectable<C,E> selectable,
 Reducer<C,E> r,
 BiFunction<? super List<? extends E>,? super C,? extends E> fh,
 BiFunction<? super C,Function<C,E>,? extends E> cache)

Returns a Reducible implementation that uses the supplied Reducer for its reduction operations and the supplied computeIfAbsent BiFunction for its caching implementation.

Type Parameters:

C - the criteria type

E - the element type

Parameters:

selectable - a Selectable; must not be null

r - a Reducer; must not be null

fh - a BiFunction serving as the supplied Reducer's failure handler; must not be null

cache - a BiFunction with the same semantics as the Map.computeIfAbsent(Object, java.util.function.Function) method; must not be null

Returns:

a Reducible; never null

Throws:

NullPointerException - if any argument is null

See Also:

• of(Selectable, Reducer, BiFunction)
• Map.computeIfAbsent(Object, java.util.function.Function)