sirius.kernel.commons

Class Lambdas

java.lang.Object

sirius.kernel.commons.Lambdas

public class Lambdas
extends Object

Helper class which provides various methods to work with lambdas.

Method Summary

Modifier and Type	Method and Description
static <K> Collector<K,Map<K,Integer>,Map<K,Integer>>	groupAndCount() Can be used to group a given stream by identity and count the occurrences of each entity.
static <T,C extends Collection<T>> Collector<T,?,C>	into(C collection) Used to collect the results of a stream operation into an existing collection.
static <T> Function<T,T>	touch(Consumer<T> consumer) Provides an identity function which permits to "touch" the element for which it was called.
static <O> O	unsupportedBiOperation(O a, O b) Can be used as lambda for unsupported BiOperations.

Methods inherited from class java.lang.Object

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

Method Detail

touch

public static <T> Function<T,T> touch(Consumer<T> consumer)

Provides an identity function which permits to "touch" the element for which it was called.

This is designed to be used with Optional like this: return Optional.of("Test").map(Lambdas.touch(s -> System.out.println(s)))

Type Parameters:

T - the type of the elements accepted by the consumer

Parameters:

consumer - the lambda used to "touch" (use) each parameter

Returns:

an identity function which also applies the consumer on each parameter

into

public static <T,C extends Collection<T>> Collector<T,?,C> into(C collection)

Used to collect the results of a stream operation into an existing collection.

Type Parameters:

T - the type of the elements accepted by the collector

C - the type of the collection which is filled by the collector

Parameters:

collection - the target collection

Returns:

a Collector inserting all elements into the given collection

groupAndCount

public static <K> Collector<K,Map<K,Integer>,Map<K,Integer>> groupAndCount()

Can be used to group a given stream by identity and count the occurrences of each entity.

Type Parameters:

K - the type of the key by which the values are grouped

Returns:

a Collector which can be supplied to Stream.collect(java.util.stream.Collector).

unsupportedBiOperation

public static <O> O unsupportedBiOperation(O a,
                                           O b)

Can be used as lambda for unsupported BiOperations.

This is intended to be a dummy parameter (e.g. for Collector.of. It will always throw an UnsupportedOperationException if invoked.

Type Parameters:

O - the type of objects for which the operation is to be used

Parameters:

a - the first parameter of the binary operation

b - the second parameter of the binary operation

Returns:

this method will never return a value as an UnsupportedOperationException is thrown

Throws:

UnsupportedOperationException - always thrown by this method