Package org.jivesoftware.util

Class CollectionUtils

java.lang.Object

org.jivesoftware.util.CollectionUtils

public class CollectionUtils
extends Object

A utility class that provides re-usable functionality that relates to Java collections.

Author:

Guus der Kinderen, guus.der.kinderen@gmail.com

Constructor Summary

Constructors

Constructor	Description
CollectionUtils()

Method Summary

Modifier and Type	Method	Description
static <T> Predicate<T>	distinctByKey(Function<? super T,Object> keyExtractor)	Returns a stateful stream filter that, once applied to a stream, returns a stream consisting of the distinct elements (according to the specified key).
static <V> Set<V>	findDuplicates(Collection<V>... collections)	Returns all elements that occur more than exactly once in the combination of all elements from all provided collections.

Methods inherited from class java.lang.Object

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

Constructor Details

CollectionUtils

public CollectionUtils()

Method Details

distinctByKey

public static <T> Predicate<T> distinctByKey(Function<? super T,Object> keyExtractor)

Returns a stateful stream filter that, once applied to a stream, returns a stream consisting of the distinct elements (according to the specified key).

The implementation of Stream.distinct() can be used to return a stream that has distinct elements, based on the implementation of Object.equals(Object). That implementation does not allow to filter a stream based on one property of each object. The implementation of provided by this method does.

Type Parameters:

T - Stream element type.

Parameters:

keyExtractor - A function to extract the desired key from the stream objects (cannot be null).

Returns:

A filter

See Also:

• Stack Overflow: Java Lambda Stream Distinct() on arbitrary key?

findDuplicates

@Nonnull
public static <V> Set<V> findDuplicates(@Nonnull
 Collection<V>... collections)

Returns all elements that occur more than exactly once in the combination of all elements from all provided collections.

Type Parameters:

V - The type of the entities in the collections.

Parameters:

collections - The collection for which to return duplicates

Returns:

The duplicates