/*
* Copyright (c) 2012, 2013, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License version 2 only, as
* published by the Free Software Foundation. Oracle designates this
* particular file as subject to the "Classpath" exception as provided
* by Oracle in the LICENSE file that accompanied this code.
*
* This code is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
* You should have received a copy of the GNU General Public License version
* 2 along with this work; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
*
* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
* or visit www.oracle.com if you need additional information or have any
* questions.
*/
package java.util.stream;
import java.util.HashSet;
import java.util.LinkedHashSet;
import java.util.Objects;
import java.util.Set;
import java.util.Spliterator;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.atomic.AtomicBoolean;
import java.util.function.IntFunction;
/**
* Factory methods for transforming streams into duplicate-free streams, using
* {@link Object#equals(Object)} to determine equality.
*
* @since 1.8
*/
final class DistinctOps {
private DistinctOps() { }
/**
* Appends a "distinct" operation to the provided stream, and returns the
* new stream.
*
* @param <T> the type of both input and output elements
* @param upstream a reference stream with element type T
* @return the new stream
*/
static <T> ReferencePipeline<T, T> makeRef(AbstractPipeline<?, T, ?> upstream) {
return new ReferencePipeline.StatefulOp<T, T>(upstream, StreamShape.REFERENCE,
StreamOpFlag.IS_DISTINCT | StreamOpFlag.NOT_SIZED) {
<P_IN> Node<T> reduce(PipelineHelper<T> helper, Spliterator<P_IN> spliterator) {
// If the stream is SORTED then it should also be ORDERED so the following will also
// preserve the sort order
TerminalOp<T, LinkedHashSet<T>> reduceOp
= ReduceOps.<T, LinkedHashSet<T>>makeRef(LinkedHashSet::new, LinkedHashSet::add,
LinkedHashSet::addAll);
return Nodes.node(reduceOp.evaluateParallel(helper, spliterator));
}
@Override
<P_IN> Node<T> opEvaluateParallel(PipelineHelper<T> helper,
Spliterator<P_IN> spliterator,
IntFunction<T[]> generator) {
if (StreamOpFlag.DISTINCT.isKnown(helper.getStreamAndOpFlags())) {
// No-op
return helper.evaluate(spliterator, false, generator);
}
else if (StreamOpFlag.ORDERED.isKnown(helper.getStreamAndOpFlags())) {
return reduce(helper, spliterator);
}
else {
// Holder of null state since ConcurrentHashMap does not support null values
AtomicBoolean seenNull = new AtomicBoolean(false);
ConcurrentHashMap<T, Boolean> map = new ConcurrentHashMap<>();
TerminalOp<T, Void> forEachOp = ForEachOps.makeRef(t -> {
if (t == null)
seenNull.set(true);
else
map.putIfAbsent(t, Boolean.TRUE);
}, false);
forEachOp.evaluateParallel(helper, spliterator);
// If null has been seen then copy the key set into a HashSet that supports null values
// and add null
Set<T> keys = map.keySet();
if (seenNull.get()) {
// TODO Implement a more efficient set-union view, rather than copying
keys = new HashSet<>(keys);
keys.add(null);
}
return Nodes.node(keys);
}
}
@Override
<P_IN> Spliterator<T> opEvaluateParallelLazy(PipelineHelper<T> helper, Spliterator<P_IN> spliterator) {
if (StreamOpFlag.DISTINCT.isKnown(helper.getStreamAndOpFlags())) {
// No-op
return helper.wrapSpliterator(spliterator);
}
else if (StreamOpFlag.ORDERED.isKnown(helper.getStreamAndOpFlags())) {
// Not lazy, barrier required to preserve order
return reduce(helper, spliterator).spliterator();
}
else {
// Lazy
return new StreamSpliterators.DistinctSpliterator<>(helper.wrapSpliterator(spliterator));
}
}
@Override
Sink<T> opWrapSink(int flags, Sink<T> sink) {
Objects.requireNonNull(sink);
if (StreamOpFlag.DISTINCT.isKnown(flags)) {
return sink;
} else if (StreamOpFlag.SORTED.isKnown(flags)) {
return new Sink.ChainedReference<T, T>(sink) {
boolean seenNull;
T lastSeen;
@Override
public void begin(long size) {
seenNull = false;
lastSeen = null;
downstream.begin(-1);
}
@Override
public void end() {
seenNull = false;
lastSeen = null;
downstream.end();
}
@Override
public void accept(T t) {
if (t == null) {
if (!seenNull) {
seenNull = true;
downstream.accept(lastSeen = null);
}
} else if (lastSeen == null || !t.equals(lastSeen)) {
downstream.accept(lastSeen = t);
}
}
};
} else {
return new Sink.ChainedReference<T, T>(sink) {
Set<T> seen;
@Override
public void begin(long size) {
seen = new HashSet<>();
downstream.begin(-1);
}
@Override
public void end() {
seen = null;
downstream.end();
}
@Override
public void accept(T t) {
if (!seen.contains(t)) {
seen.add(t);
downstream.accept(t);
}
}
};
}
}
};
}
}