Package org.apache.druid.utils

Class CollectionUtils

java.lang.Object

org.apache.druid.utils.CollectionUtils

public final class CollectionUtils
extends Object

Method Summary

Modifier and Type	Method	Description
static <E> Collection<E>	createLazyCollectionFromStream(Supplier<Stream<E>> sequentialStreamSupplier, int size)	Returns a lazy collection from a stream supplier and a size.
static <T, I extends Iterable<T>, X extends Throwable> T	getOnlyElement(I iterable, Function<? super I,? extends X> exceptionSupplier)	Like Iterables.getOnlyElement(Iterable), but allows a customizable error message.
static <T> Set<T>	intersect(Set<T> left, Set<T> right)	Intersection of two sets: C = A ∩ B.
static boolean	isNullOrEmpty(Collection<?> list)
static <K, V, K2> Map<K2,V>	mapKeys(Map<K,V> map, Function<K,K2> keyMapper)	Returns a transformed map from the given input map where the key is modified based on the given keyMapper function.
static <K, V, V2> Map<K,V2>	mapValues(Map<K,V> map, Function<V,V2> valueMapper)	Returns a transformed map from the given input map where the value is modified based on the given valueMapper function.
static <K, V> LinkedHashMap<K,V>	newLinkedHashMapWithExpectedSize(int expectedSize)	Returns a LinkedHashMap with an appropriate size based on the callers expectedSize.
static <E> TreeSet<E>	newTreeSet(Comparator<? super E> comparator, Iterable<E> elements)
static <T> Set<T>	subtract(Set<T> left, Set<T> right)	Subtract one set from another: C = A - B.
static <E, K, V> Map<K,V>	toMap(Collection<E> collection, Function<E,K> keyMapper, Function<E,V> valueMapper)	Creates an immutable map by mapping each entry in the given collection to a key and a value.
static <T> Set<T>	union(Set<T> left, Set<T> right)	Union of two sets: C = A ∪ B.

Methods inherited from class java.lang.Object

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

Method Details

createLazyCollectionFromStream

public static <E> Collection<E> createLazyCollectionFromStream(Supplier<Stream<E>> sequentialStreamSupplier,
 int size)

Returns a lazy collection from a stream supplier and a size. Collection.iterator() of the returned collection delegates to BaseStream.iterator() on the stream returned from the supplier.

newTreeSet

public static <E> TreeSet<E> newTreeSet(Comparator<? super E> comparator,
 Iterable<E> elements)

mapValues

public static <K,
V,
V2> Map<K,V2> mapValues(Map<K,V> map,
 Function<V,V2> valueMapper)

Returns a transformed map from the given input map where the value is modified based on the given valueMapper function. Unlike Maps.transformValues(java.util.Map<K, V1>, com.google.common.base.Function<? super V1, V2>), this method applies the mapping function eagerly to all key-value pairs in the source map and returns a new HashMap, while Maps.transformValues(java.util.Map<K, V1>, com.google.common.base.Function<? super V1, V2>) returns a lazy map view.

mapKeys

public static <K,
V,
K2> Map<K2,V> mapKeys(Map<K,V> map,
 Function<K,K2> keyMapper)

Returns a transformed map from the given input map where the key is modified based on the given keyMapper function. This method fails if keys collide after applying the given keyMapper function and throws a IllegalStateException.

Throws:

ISE - if key collisions occur while applying specified keyMapper

toMap

public static <E,
K,
V> Map<K,V> toMap(Collection<E> collection,
 Function<E,K> keyMapper,
 Function<E,V> valueMapper)

Creates an immutable map by mapping each entry in the given collection to a key and a value.

newLinkedHashMapWithExpectedSize

public static <K,
V> LinkedHashMap<K,V> newLinkedHashMapWithExpectedSize(int expectedSize)

Returns a LinkedHashMap with an appropriate size based on the callers expectedSize. This methods functionality mirrors that of com.google.common.collect.Maps#newLinkedHashMapWithExpectedSize in Guava 19+. Thus, this method can be replaced with Guava's implementation once Druid has upgraded its Guava dependency to a sufficient version.

Parameters:

expectedSize - the expected size of the LinkedHashMap

Returns:

LinkedHashMap object with appropriate size based on callers expectedSize

isNullOrEmpty

public static boolean isNullOrEmpty(@Nullable
 Collection<?> list)

subtract

public static <T> Set<T> subtract(Set<T> left,
 Set<T> right)

Subtract one set from another: C = A - B.

intersect

public static <T> Set<T> intersect(Set<T> left,
 Set<T> right)

Intersection of two sets: C = A ∩ B.

union

public static <T> Set<T> union(Set<T> left,
 Set<T> right)

Union of two sets: C = A ∪ B.

getOnlyElement

public static <T,
I extends Iterable<T>,
X extends Throwable>
T getOnlyElement(I iterable,
 Function<? super I,? extends X> exceptionSupplier)
          throws X

Like Iterables.getOnlyElement(Iterable), but allows a customizable error message.

Throws:

X