org.whaka.util.function

Class MapCollectors

java.lang.Object

org.whaka.util.function.MapCollectors

public class MapCollectors
extends java.lang.Object

Class provides static factory methods to create Collector instances to transform streams into maps.

Main differences from Collectors.toMap methods are:

• This class doesn't use Map.merge(Object, Object, java.util.function.BiFunction) method and instead performs all merging "manually", using "containsKey", "get", and "put". Note! This means that both elements of a merging function might be nulls!
  
  
• Default merging function doesn't throw an exception. Instead it replaces old value with the new one. (The same, as if "put" method would be used.) See: replacingMerger()

Also there're collector factories specifically for stream of map entries: toMap() or toMap(Supplier)

Method Summary

Modifier and Type	Method and Description
static <V> java.util.function.BinaryOperator<V>	replacingMerger() Creates a binary operator that always returns second argument.
static <K,V> java.util.stream.Collector<java.util.Map.Entry<K,V>,?,java.util.Map<K,V>>	toMap() Create new collector that will collect stream of map entries into a default map.
static <T,K,V> java.util.stream.Collector<T,?,java.util.Map<K,V>>	toMap(java.util.function.Function<? super T,? extends K> keyMapper, java.util.function.Function<? super T,? extends V> valueMapper) Map each element of the a stream into key/value pair by specified functions.
static <T,K,V> java.util.stream.Collector<T,?,java.util.Map<K,V>>	toMap(java.util.function.Function<? super T,? extends K> keyMapper, java.util.function.Function<? super T,? extends V> valueMapper, java.util.function.BinaryOperator<V> mergeFunction) Map each element of the a stream into key/value pair by specified functions.
static <T,K,V,M extends java.util.Map<K,V>> java.util.stream.Collector<T,?,M>	toMap(java.util.function.Function<? super T,? extends K> keyMapper, java.util.function.Function<? super T,? extends V> valueMapper, java.util.function.BinaryOperator<V> mergeFunction, java.util.function.Supplier<M> mapSupplier) Map each element of the a stream into key/value pair by specified functions.
static <T,K,V,M extends java.util.Map<K,V>> java.util.stream.Collector<T,?,M>	toMap(java.util.function.Function<? super T,? extends K> keyMapper, java.util.function.Function<? super T,? extends V> valueMapper, java.util.function.Supplier<M> mapSupplier) Map each element of the a stream into key/value pair by specified functions.
static <K,V,M extends java.util.Map<K,V>> java.util.stream.Collector<java.util.Map.Entry<K,V>,?,M>	toMap(java.util.function.Supplier<M> mapSupplier) Create new collector that will collect stream of map entries into a map provided by the specified supplier.

Methods inherited from class java.lang.Object

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

Method Detail

toMap

public static <K,V> java.util.stream.Collector<java.util.Map.Entry<K,V>,?,java.util.Map<K,V>> toMap()

Create new collector that will collect stream of map entries into a default map. No additional parameters are required, for map entries are naturally suitable for a map.

See Also:

toMap(Supplier)

toMap

public static <K,V,M extends java.util.Map<K,V>> java.util.stream.Collector<java.util.Map.Entry<K,V>,?,M> toMap(java.util.function.Supplier<M> mapSupplier)

Create new collector that will collect stream of map entries into a map provided by the specified supplier. No additional parameters are required, for map entries are naturally suitable for a map.

See Also:

toMap()

toMap

public static <T,K,V> java.util.stream.Collector<T,?,java.util.Map<K,V>> toMap(java.util.function.Function<? super T,? extends K> keyMapper,
                                                                               java.util.function.Function<? super T,? extends V> valueMapper)

Map each element of the a stream into key/value pair by specified functions. Then collect them into a default map. Any key collisions will be replaced with latter value.

See Also:

toMap(Function, Function, Supplier), toMap(Function, Function, BinaryOperator), toMap(Function, Function, BinaryOperator, Supplier)

toMap

public static <T,K,V> java.util.stream.Collector<T,?,java.util.Map<K,V>> toMap(java.util.function.Function<? super T,? extends K> keyMapper,
                                                                               java.util.function.Function<? super T,? extends V> valueMapper,
                                                                               java.util.function.BinaryOperator<V> mergeFunction)

Map each element of the a stream into key/value pair by specified functions. Then collect them into a default map. Any key collisions will be resolved by the specified merge function.

See Also:

toMap(Function, Function), toMap(Function, Function, Supplier), toMap(Function, Function, BinaryOperator, Supplier)

toMap

public static <T,K,V,M extends java.util.Map<K,V>> java.util.stream.Collector<T,?,M> toMap(java.util.function.Function<? super T,? extends K> keyMapper,
                                                                                           java.util.function.Function<? super T,? extends V> valueMapper,
                                                                                           java.util.function.Supplier<M> mapSupplier)

Map each element of the a stream into key/value pair by specified functions. Then collect them into a map provided by the specified supplier. Any key collisions will be replaced with latter value.

See Also:

toMap(Function, Function), toMap(Function, Function, BinaryOperator), toMap(Function, Function, BinaryOperator, Supplier)

toMap

public static <T,K,V,M extends java.util.Map<K,V>> java.util.stream.Collector<T,?,M> toMap(java.util.function.Function<? super T,? extends K> keyMapper,
                                                                                           java.util.function.Function<? super T,? extends V> valueMapper,
                                                                                           java.util.function.BinaryOperator<V> mergeFunction,
                                                                                           java.util.function.Supplier<M> mapSupplier)

Map each element of the a stream into key/value pair by specified functions. Then collect them into a map provided by the specified supplier. Any key collisions will be resolved by the specified merge function.

See Also:

toMap(Function, Function), toMap(Function, Function, Supplier), toMap(Function, Function, BinaryOperator)

replacingMerger

public static <V> java.util.function.BinaryOperator<V> replacingMerger()

Creates a binary operator that always returns second argument.