StreamOperations.java
/*
* *********************************************************************************************************************
*
* TheseFoolishThings: Miscellaneous utilities
* http://tidalwave.it/projects/thesefoolishthings
*
* Copyright (C) 2009 - 2021 by Tidalwave s.a.s. (http://tidalwave.it)
*
* *********************************************************************************************************************
*
* Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on
* an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the
* specific language governing permissions and limitations under the License.
*
* *********************************************************************************************************************
*
* git clone https://bitbucket.org/tidalwave/thesefoolishthings-src
* git clone https://github.com/tidalwave-it/thesefoolishthings-src
*
* *********************************************************************************************************************
*/
package it.tidalwave.util;
import javax.annotation.Nonnull;
import java.util.Iterator;
import java.util.Spliterator;
import java.util.Spliterators;
import java.util.function.BiFunction;
import java.util.function.Consumer;
import java.util.stream.Stream;
import java.util.stream.StreamSupport;
import lombok.AccessLevel;
import lombok.NoArgsConstructor;
/***********************************************************************************************************************
*
* A collection of operations on {@link Stream}s.
*
* @author Fabrizio Giudici
* @since 3.2-ALPHA-12
* @it.tidalwave.javadoc.draft
*
**********************************************************************************************************************/
@NoArgsConstructor(access = AccessLevel.PRIVATE)
public final class StreamOperations
{
/*******************************************************************************************************************
*
* Zips two streams into a stream of {@link Pair}s.
*
* @param streamA the first {@link Stream}
* @param streamB the second {@link Stream}
* @param <A> the type of elements of the first {@link Stream}
* @param <B> the type of elements of the second {@link Stream}
* @return the zipped {@link Stream}
* @since 3.2-ALPHA-12
*
******************************************************************************************************************/
@Nonnull
public static <A, B> Stream<Pair<A, B>> zip (@Nonnull final Stream<? extends A> streamA,
@Nonnull final Stream<? extends B> streamB)
{
return zip(streamA, streamB, Pair::of);
}
/*******************************************************************************************************************
*
* Zips two streams.
*
* @param streamA the first {@link Stream}
* @param streamB the second {@link Stream}
* @param zipper the zipping function
* @param <A> the type of elements of the first {@link Stream}
* @param <B> the type of elements of the second {@link Stream}
* @param <R> the type of elements of the zipped {@link Stream}
* @return the zipped {@link Stream}
* @since 3.2-ALPHA-12
*
******************************************************************************************************************/
@Nonnull
public static <A, B, R> Stream<R> zip (@Nonnull final Stream<A> streamA,
@Nonnull final Stream<B> streamB,
@Nonnull final BiFunction<? super A, ? super B, ? extends R> zipper)
{
final boolean parallel = streamA.isParallel() || streamB.isParallel();
final Spliterator<A> sa = streamA.spliterator();
final Spliterator<B> sb = streamB.spliterator();
final int characteristics =
sa.characteristics() & sb.characteristics() & (Spliterator.SIZED | Spliterator.ORDERED);
final Iterator<A> a = Spliterators.iterator(sa);
final Iterator<B> b = Spliterators.iterator(sb);
final long estSize = Math.min(sa.estimateSize(), sb.estimateSize());
return StreamSupport.stream(new Spliterators.AbstractSpliterator<R>(estSize, characteristics)
{
@Override
public boolean tryAdvance (@Nonnull final Consumer<? super R> action)
{
if (a.hasNext() && b.hasNext())
{
action.accept(zipper.apply(a.next(), b.next()));
return true;
}
return false;
}
},
parallel)
.onClose(streamA::close)
.onClose(streamB::close);
}
}