Class CollectionUtils

java.lang.Object

org.junit.platform.commons.util.CollectionUtils

@API(status=INTERNAL,
     since="1.0")
public final class CollectionUtils
extends Object

Collection of utilities for working with Collections.

DISCLAIMER

These utilities are intended solely for usage within the JUnit framework itself. Any usage by external parties is not supported. Use at your own risk!

Since:

1.0

Method Summary

Modifier and Type	Method	Description
static <T extends @Nullable Object> void	forEachInReverseOrder(List<T> list, Consumer<? super T> action)	Call the supplied action on each element of the supplied List from last to first element.
static <T extends @Nullable Object> Optional<T>	getFirstElement(Collection<T> collection)	Get the first element of the supplied collection unless it's empty.
static <T> T	getOnlyElement(Collection<T> collection)	Get the only element of a collection of size 1.
static boolean	isConvertibleToStream(@Nullable Class<?> type)	Determine if an instance of the supplied type can be converted into a Stream.
static Stream<?>	toStream(Object object)	Convert an object of one of the following supported types into a Stream.

Methods inherited from class java.lang.Object

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

Method Details

getOnlyElement

public static <T> T getOnlyElement(Collection<T> collection)

Get the only element of a collection of size 1.

Parameters:

collection - the collection to get the element from

Returns:

the only element of the collection

Throws:

PreconditionViolationException - if the collection is null or does not contain exactly one element

getFirstElement

@API(status=INTERNAL,
     since="1.11")
public static <T extends @Nullable Object>
Optional<T> getFirstElement(Collection<T> collection)

Get the first element of the supplied collection unless it's empty.

Parameters:

collection - the collection to get the element from

Returns:

the first element of the collection; empty if the collection is empty

Throws:

PreconditionViolationException - if the collection is null

Since:

1.11

isConvertibleToStream

@API(status=INTERNAL,
     since="1.9.1")
public static boolean isConvertibleToStream(@Nullable Class<?> type)

Determine if an instance of the supplied type can be converted into a Stream.

If this method returns true, toStream(Object) can successfully convert an object of the specified type into a stream. See toStream(Object) for supported types.

Parameters:

type - the type to check; may be null

Returns:

true if an instance of the type can be converted into a stream

Since:

1.9.1

See Also:

• toStream(Object)

toStream

public static Stream<?> toStream(Object object)

Convert an object of one of the following supported types into a Stream.

• Stream
• DoubleStream
• IntStream
• LongStream
• Collection
• Iterable
• Iterator
• Object array
• primitive array
• any type that provides an Iterator-returning iterator() method (such as, for example, a kotlin.sequences.Sequence)

Parameters:

object - the object to convert into a stream; never null

Returns:

the resulting stream

Throws:

PreconditionViolationException - if the supplied object is null or not one of the supported types

See Also:

• isConvertibleToStream(Class)

forEachInReverseOrder

@API(status=INTERNAL,
     since="1.9.2")
public static <T extends @Nullable Object> void forEachInReverseOrder(List<T> list,
 Consumer<? super T> action)

Call the supplied action on each element of the supplied List from last to first element.