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/*
* Copyright 2016 Google Inc.
*
* 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.
*/
package java.util.stream;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Comparator;
import java.util.DoubleSummaryStatistics;
import java.util.HashMap;
import java.util.HashSet;
import java.util.IntSummaryStatistics;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.LongSummaryStatistics;
import java.util.Map;
import java.util.Optional;
import java.util.Set;
import java.util.StringJoiner;
import java.util.function.BiConsumer;
import java.util.function.BinaryOperator;
import java.util.function.Function;
import java.util.function.Predicate;
import java.util.function.Supplier;
import java.util.function.ToDoubleFunction;
import java.util.function.ToIntFunction;
import java.util.function.ToLongFunction;
/**
* See the
* official Java API doc for details.
*/
public final class Collectors {
public static Collector averagingDouble(ToDoubleFunction mapper) {
// TODO simplify to only collect average if possible
return collectingAndThen(summarizingDouble(mapper), DoubleSummaryStatistics::getAverage);
}
public static Collector averagingInt(ToIntFunction mapper) {
// TODO simplify to only collect average if possible
return collectingAndThen(summarizingInt(mapper), IntSummaryStatistics::getAverage);
}
public static Collector averagingLong(ToLongFunction mapper) {
// TODO simplify to only collect average if possible
return collectingAndThen(summarizingLong(mapper), LongSummaryStatistics::getAverage);
}
public static Collector collectingAndThen(
Collector downstream, Function finisher) {
return new CollectorImpl<>(
downstream.supplier(),
downstream.accumulator(),
downstream.combiner(),
downstream.finisher().andThen(finisher));
}
public static Collector counting() {
// Using Long::sum here fails in JDT
return reducing(0L, item -> 1L, (a, b) -> (Long) a.longValue() + b.longValue());
}
public static Collector>> groupingBy(
Function classifier) {
// TODO inline this and avoid the finisher extra work of copying from a map to another map
// kept separate for now to unify implementations and reduce testing required
return groupingBy(classifier, toList());
}
public static Collector> groupingBy(
Function classifier, Collector downstream) {
return groupingBy(classifier, HashMap::new, downstream);
}
public static > Collector groupingBy(
Function classifier,
Supplier mapFactory,
Collector downstream) {
return groupingBy0(() -> {
// cannot use LinkedHashMap::new because javac cannot infer correct
// return type of method reference
return new LinkedHashMap<>();
}, classifier, mapFactory, downstream);
}
private static > Collector groupingBy0(
Supplier>> supplier,
Function classifier,
Supplier mapFactory,
Collector downstream) {
return Collector.of(
supplier,
(m, o) -> {
K k = classifier.apply(o);
List l = m.get(k);
if (l == null) {
l = new ArrayList<>();
m.put(k, l);
}
l.add(o);
},
(m1, m2) -> mergeAll(m1, m2, Collectors::addAll),
m -> {
M result = mapFactory.get();
for (Map.Entry> entry : m.entrySet()) {
result.put(entry.getKey(), streamAndCollect(downstream, entry.getValue()));
}
return result;
});
}
// not supported
// public static Collector>> groupingByConcurrent(
// Function classifier)
// public static Collector> groupingByConcurrent(
// Function classifier, Collector downstream)
// public static > Collector groupingByConcurrent(
// Function classifier, Supplier mapFactory,
// Collector downstream)
public static Collector joining() {
// specific implementation rather than calling joining("") since we don't need to worry about
// appending delimiters between empty strings
return Collector.of(
StringBuilder::new,
StringBuilder::append,
StringBuilder::append,
StringBuilder::toString
);
}
public static Collector joining(CharSequence delimiter) {
return joining(delimiter, "", "");
}
public static Collector joining(
final CharSequence delimiter, CharSequence prefix, CharSequence suffix) {
return Collector.of(
() -> new StringJoiner(delimiter, prefix, suffix),
StringJoiner::add,
StringJoiner::merge,
StringJoiner::toString
);
}
public static Collector mapping(
final Function mapper, final Collector downstream) {
return new CollectorImpl<>(
downstream.supplier(),
(BiConsumer)
(A a, T t) -> {
downstream.accumulator().accept(a, mapper.apply(t));
},
downstream.combiner(),
downstream.finisher());
}
public static Collector> maxBy(Comparator comparator) {
return reducing(BinaryOperator.maxBy(comparator));
}
public static Collector> minBy(final Comparator comparator) {
return reducing(BinaryOperator.minBy(comparator));
}
public static Collector>> partitioningBy(
Predicate predicate) {
return partitioningBy(predicate, toList());
}
public static Collector> partitioningBy(
Predicate predicate, Collector downstream) {
return groupingBy0(partitionSupplier(), predicate::test, HashMap::new, downstream);
}
private static Supplier>> partitionSupplier() {
return () -> {
Map> partition = new LinkedHashMap<>();
partition.put(false, new ArrayList<>());
partition.put(true, new ArrayList<>());
return partition;
};
}
public static Collector> reducing(BinaryOperator op) {
return reducing(Optional.empty(), Optional::of, (a, b) -> {
if (!a.isPresent()) {
return b;
}
if (!b.isPresent()) {
return a;
}
return Optional.of(op.apply(a.get(), b.get()));
});
}
public static Collector reducing(T identity, BinaryOperator op) {
return reducing(identity, Function.identity(), op);
}
@SuppressWarnings("unchecked")
public static Collector reducing(
final U identity, final Function mapper, BinaryOperator op) {
return Collector.of(
() -> new Object[]{identity},
(u, t) -> u[0] = op.apply((U) u[0], mapper.apply(t)),
(Object[] u1, Object[] u2) -> {
u1[0] = op.apply((U) u1[0], (U) u2[0]);
return u1;
},
(Object[] a) -> (U) a[0]
);
}
public static Collector summarizingDouble(
ToDoubleFunction mapper) {
return Collector.of(
DoubleSummaryStatistics::new,
(stats, item) -> stats.accept(mapper.applyAsDouble(item)),
(t, u) -> {
t.combine(u);
return t;
},
Collector.Characteristics.UNORDERED, Collector.Characteristics.IDENTITY_FINISH
);
}
public static Collector summarizingInt(
ToIntFunction mapper) {
return Collector.of(
IntSummaryStatistics::new,
(stats, item) -> stats.accept(mapper.applyAsInt(item)),
(t, u) -> {
t.combine(u);
return t;
},
Collector.Characteristics.UNORDERED, Collector.Characteristics.IDENTITY_FINISH
);
}
public static Collector summarizingLong(
ToLongFunction mapper) {
return Collector.of(
LongSummaryStatistics::new,
(stats, item) -> stats.accept(mapper.applyAsLong(item)),
(t, u) -> {
t.combine(u);
return t;
},
Collector.Characteristics.UNORDERED, Collector.Characteristics.IDENTITY_FINISH
);
}
public static Collector summingDouble(final ToDoubleFunction mapper) {
// TODO simplify to only collect sum if possible
return collectingAndThen(summarizingDouble(mapper), DoubleSummaryStatistics::getSum);
}
public static Collector summingInt(ToIntFunction mapper) {
// TODO simplify to only collect sum if possible
return collectingAndThen(
summarizingInt(mapper), intSummaryStatistics -> (int) intSummaryStatistics.getSum());
}
public static Collector summingLong(ToLongFunction mapper) {
// TODO simplify to only collect sum if possible
return collectingAndThen(summarizingLong(mapper), LongSummaryStatistics::getSum);
}
public static > Collector toCollection(
final Supplier collectionFactory) {
return Collector.of(
collectionFactory,
Collection::add,
// TODO switch to a lambda reference once #9333 is fixed
(c1, c2) -> addAll(c1, c2),
Collector.Characteristics.IDENTITY_FINISH
);
}
// not supported
// public static Collector> toConcurrentMap(
// Function keyMapper, Function valueMapper)
// public static Collector> toConcurrentMap(
// Function keyMapper, Function valueMapper,
// BinaryOperator mergeFunction)
// public static > Collector toConcurrentMap(
// Function keyMapper, Function valueMapper,
// BinaryOperator mergeFunction, Supplier mapSupplier)
public static Collector> toList() {
return toCollection(ArrayList::new);
}
public static Collector> toMap(
final Function keyMapper,
final Function valueMapper) {
return toMap(
keyMapper,
valueMapper,
(m1, m2) -> {
throw new IllegalStateException("Can't assign multiple values to the same key");
});
}
public static Collector> toMap(
Function keyMapper,
Function valueMapper,
BinaryOperator mergeFunction) {
return toMap(keyMapper, valueMapper, mergeFunction, HashMap::new);
}
public static > Collector toMap(
final Function keyMapper,
final Function valueMapper,
final BinaryOperator mergeFunction,
final Supplier mapSupplier) {
return Collector.of(
mapSupplier,
(map, item) -> {
K key = keyMapper.apply(item);
U newValue = valueMapper.apply(item);
if (map.containsKey(key)) {
map.put(key, mergeFunction.apply(map.get(key), newValue));
} else {
map.put(key, newValue);
}
},
(m1, m2) -> mergeAll(m1, m2, mergeFunction),
Collector.Characteristics.IDENTITY_FINISH);
}
public static Collector> toSet() {
return Collector., Set>of(
HashSet::new,
HashSet::add,
// TODO switch to a lambda reference once #9333 is fixed
(c1, c2) -> addAll(c1, c2),
// this is Function.identity, but Java doesn't like it here to change types.
s -> s,
Collector.Characteristics.UNORDERED, Collector.Characteristics.IDENTITY_FINISH
);
}
private static D streamAndCollect(Collector downstream, List list) {
A a = downstream.supplier().get();
for (T t : list) {
downstream.accumulator().accept(a, t);
}
return downstream.finisher().apply(a);
}
private static > M mergeAll(
M m1, M m2, BinaryOperator mergeFunction) {
for (Map.Entry entry : m2.entrySet()) {
m1.merge(entry.getKey(), entry.getValue(), mergeFunction);
}
return m1;
}
private static > C addAll(C collection, Collection items) {
collection.addAll(items);
return collection;
}
private Collectors() { }
}