Module org.junit.platform.commons
Package org.junit.platform.commons.util

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 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> 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

    • toSet

      @API(status=INTERNAL, since="1.6") public static <T> Set<T> toSet(T[] values)
      Convert the supplied array of values to a Set.
      Parameters:
      values - the array of values; never null
      Returns:
      a set of the values
      Throws:
      PreconditionViolationException - if the array is null
      Since:
      1.6

    • toUnmodifiableList

      public static <T> Collector<T,?,List<T>> toUnmodifiableList()
      Return a Collector that accumulates the input elements into a new unmodifiable list, in encounter order.

      There are no guarantees on the type or serializability of the list returned, so if more control over the returned list is required, consider creating a new Collector implementation like the following: 

       public static <T> Collector<T, ?, List<T>> toUnmodifiableList(Supplier<List<T>> listSupplier) {
     return Collectors.collectingAndThen(Collectors.toCollection(listSupplier), Collections::unmodifiableList);
 }
      Type Parameters:
      T - the type of the input elements
      Returns:
      a Collector which collects all the input elements into an unmodifiable list, in encounter order

    • isConvertibleToStream

      @API(status=INTERNAL, since="1.9.1") public static boolean isConvertibleToStream(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

      public static Stream<?> toStream(Object object)
      Convert an object of one of the following supported types into a Stream.
      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:

    • forEachInReverseOrder

      @API(status=INTERNAL, since="1.9.2") public static <T> 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.