org.apache.flink.util

Class CollectionUtil

java.lang.Object

org.apache.flink.util.CollectionUtil

@Internal
public final class CollectionUtil
extends Object

Simple utility to work with Java collections.

Field Summary

Fields

Modifier and Type	Field and Description
static int	MAX_ARRAY_SIZE A safe maximum size for arrays in the JVM.

Method Summary

Modifier and Type	Method and Description
static <T> Collection<T>	checkedSubTypeCast(Collection<? super T> collection, Class<T> subTypeClass) Casts the given collection to a subtype.
static <K,V> Map.Entry<K,V>	entry(K k, V v) Returns an immutable Map.Entry.
static boolean	isEmptyOrAllElementsNull(Collection<?> collection) Returns true if the given collection is empty or contains only null elements.
static boolean	isNullOrEmpty(Collection<?> collection) Returns true if the given collection is null or empty.
static boolean	isNullOrEmpty(Map<?,?> map)
static <E> List<E>	iterableToList(Iterable<E> iterable) Collects the elements in the Iterable in a List.
static <E> List<E>	iteratorToList(Iterator<E> iterator) Collects the elements in the Iterator in a List.
static <K,V> Map<K,V>	map(Map.Entry<K,V>... entries) Returns an immutable Map from the provided entries.
static <T,R> Stream<R>	mapWithIndex(Collection<T> input, BiFunction<T,Integer,R> mapper)
static <K,V> HashMap<K,V>	newHashMapWithExpectedSize(int expectedSize) Creates a new HashMap of the expected size, i.e. a hash map that will not rehash if expectedSize many keys are inserted, considering the load factor.
static <E> HashSet<E>	newHashSetWithExpectedSize(int expectedSize) Creates a new HashSet of the expected size, i.e. a hash set that will not rehash if expectedSize many unique elements are inserted, considering the load factor.
static <K,V> LinkedHashMap<K,V>	newLinkedHashMapWithExpectedSize(int expectedSize) Creates a new LinkedHashMap of the expected size, i.e. a hash map that will not rehash if expectedSize many keys are inserted, considering the load factor.
static <E> LinkedHashSet<E>	newLinkedHashSetWithExpectedSize(int expectedSize) Creates a new LinkedHashSet of the expected size, i.e. a hash set that will not rehash if expectedSize many unique elements are inserted, considering the load factor.
static <T> Set<T>	ofNullable(T obj)
static <T> Collection<List<T>>	partition(Collection<T> elements, int numBuckets) Partition a collection into approximately n buckets.
static <I,O> Collection<O>	project(Collection<I> collection, Function<I,O> projector)
static <T> Collection<T>	subTypeCast(Collection<? super T> collection) Casts the given collection to a subtype.

Methods inherited from class java.lang.Object

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

Field Detail

MAX_ARRAY_SIZE

public static final int MAX_ARRAY_SIZE

A safe maximum size for arrays in the JVM.

See Also:

Constant Field Values

Method Detail

isNullOrEmpty

public static boolean isNullOrEmpty(Collection<?> collection)

Returns true if the given collection is null or empty.

isEmptyOrAllElementsNull

public static boolean isEmptyOrAllElementsNull(Collection<?> collection)

Returns true if the given collection is empty or contains only null elements.

isNullOrEmpty

public static boolean isNullOrEmpty(Map<?,?> map)

ofNullable

public static <T> Set<T> ofNullable(@Nullable
                                    T obj)

mapWithIndex

public static <T,R> Stream<R> mapWithIndex(Collection<T> input,
                                           BiFunction<T,Integer,R> mapper)

partition

public static <T> Collection<List<T>> partition(Collection<T> elements,
                                                int numBuckets)

Partition a collection into approximately n buckets.

project

public static <I,O> Collection<O> project(Collection<I> collection,
                                          Function<I,O> projector)

iterableToList

public static <E> List<E> iterableToList(@Nullable
                                         Iterable<E> iterable)

Collects the elements in the Iterable in a List. If the iterable argument is null, this method returns an empty list.

iteratorToList

public static <E> List<E> iteratorToList(@Nullable
                                         Iterator<E> iterator)

Collects the elements in the Iterator in a List. If the iterator argument is null, this method returns an empty list.

entry

public static <K,V> Map.Entry<K,V> entry(K k,
                                         V v)

Returns an immutable Map.Entry.

map

@SafeVarargs
public static <K,V> Map<K,V> map(Map.Entry<K,V>... entries)

Returns an immutable Map from the provided entries.

newHashMapWithExpectedSize

public static <K,V> HashMap<K,V> newHashMapWithExpectedSize(int expectedSize)

Creates a new HashMap of the expected size, i.e. a hash map that will not rehash if expectedSize many keys are inserted, considering the load factor.

Type Parameters:

K - the type of keys maintained by this map.

V - the type of mapped values.

Parameters:

expectedSize - the expected size of the created hash map.

Returns:

a new hash map instance with enough capacity for the expected size.

newLinkedHashMapWithExpectedSize

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

Creates a new LinkedHashMap of the expected size, i.e. a hash map that will not rehash if expectedSize many keys are inserted, considering the load factor.

Type Parameters:

K - the type of keys maintained by this map.

V - the type of mapped values.

Parameters:

expectedSize - the expected size of the created hash map.

Returns:

a new hash map instance with enough capacity for the expected size.

newHashSetWithExpectedSize

public static <E> HashSet<E> newHashSetWithExpectedSize(int expectedSize)

Creates a new HashSet of the expected size, i.e. a hash set that will not rehash if expectedSize many unique elements are inserted, considering the load factor.

Type Parameters:

E - the type of elements stored by this set.

Parameters:

expectedSize - the expected size of the created hash map.

Returns:

a new hash map instance with enough capacity for the expected size.

newLinkedHashSetWithExpectedSize

public static <E> LinkedHashSet<E> newLinkedHashSetWithExpectedSize(int expectedSize)

Creates a new LinkedHashSet of the expected size, i.e. a hash set that will not rehash if expectedSize many unique elements are inserted, considering the load factor.

Type Parameters:

E - the type of elements stored by this set.

Parameters:

expectedSize - the expected size of the created hash map.

Returns:

a new hash map instance with enough capacity for the expected size.

subTypeCast

public static <T> Collection<T> subTypeCast(Collection<? super T> collection)

Casts the given collection to a subtype. This is an unchecked cast that can lead to runtime exceptions.

Type Parameters:

T - the subtype to cast to.

Parameters:

collection - the collection to cast.

Returns:

the collection unchecked-cast to a subtype.

checkedSubTypeCast

public static <T> Collection<T> checkedSubTypeCast(Collection<? super T> collection,
                                                   Class<T> subTypeClass)

Casts the given collection to a subtype. This is a checked cast.

Type Parameters:

T - the subtype to cast to.

Parameters:

collection - the collection to cast.

subTypeClass - the class of the subtype to cast to.

Returns:

the collection checked and cast to a subtype.