Class MoreCollectors

java.lang.Object

com.google.common.collect.MoreCollectors

@GwtCompatible
public final class MoreCollectors
extends Object

Collectors not present in java.util.stream.Collectors that are not otherwise associated with a com.google.common type.

Since:

21.0

Author:

Louis Wasserman

Method Summary

Modifier and Type	Method	Description
static <T extends @Nullable Object> Collector<T,?,T>	onlyElement()	A collector that takes a stream containing exactly one element and returns that element.
static <T> Collector<T, ?, Optional<T>>	toOptional()	A collector that converts a stream of zero or one elements to an Optional.

Methods inherited from class java.lang.Object

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

Method Details

toOptional

public static <T> Collector<T, ?, Optional<T>> toOptional()

A collector that converts a stream of zero or one elements to an Optional.

Returns:

Optional.of(onlyElement) if the stream has exactly one element (must not be null) and returns Optional.empty() if it has none.

Throws:

IllegalArgumentException - if the stream consists of two or more elements.

NullPointerException - if any element in the stream is null.

onlyElement

public static <T extends @Nullable Object>
Collector<T,?,T> onlyElement()

A collector that takes a stream containing exactly one element and returns that element. The returned collector throws an IllegalArgumentException if the stream consists of two or more elements, and a NoSuchElementException if the stream is empty.