Package io.blt.util.stream

Class SingletonCollectors

java.lang.Object

io.blt.util.stream.SingletonCollectors

public final class SingletonCollectors
extends Object

Implementations of Collector that reduce to exactly one or zero elements. e.g.,

 var maybeActiveStep = sequentialSteps.stream()
         .filter(SequentialStep::isActive)
         .collect(SingletonCollectors.toOptional());
 

If more than one element is present, then IllegalArgumentException is thrown.

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
static final class	SingletonCollectors.Container<T>
static final class	SingletonCollectors.SingletonCollector<T,R>

Method Summary

Modifier and Type	Method	Description
static <T> SingletonCollectors.SingletonCollector<T,T>	toNullable()	Returns a Collector that accumulates the only element, if any, into a nullable Object.
static <T> SingletonCollectors.SingletonCollector<T,Optional<T>>	toOptional()	Returns a Collector that accumulates the only element, if any, into an Optional.

Methods inherited from class java.lang.Object

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

Method Details

toOptional

public static <T>
SingletonCollectors.SingletonCollector<T,Optional<T>> toOptional()

Returns a Collector that accumulates the only element, if any, into an Optional.

Type Parameters:

T - the type of the input elements

Returns:

a Collector that accumulates the only element, if any, into an Optional.

Throws:

IllegalArgumentException - if more than one element is present

toNullable

public static <T>
SingletonCollectors.SingletonCollector<T,T> toNullable()

Returns a Collector that accumulates the only element, if any, into a nullable Object.

Type Parameters:

T - the type of the input elements

Returns:

a Collector that accumulates the only element, if any, into a nullable Object.

Throws:

IllegalArgumentException - if more than one element is present