MoreCollectors (Guava: Google Core Libraries for Java 31.1-jre API)

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

All Methods Static Methods Concrete Methods
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 Detail
  - 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.