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Library providing immutable/persistent collection classes for
Java. While collections are immutable they provide methods for
adding and removing values by creating new modified copies of
themselves. Each copy shares almost all of its structure with
other copies to minimize memory consumption.
///###////////////////////////////////////////////////////////////////////////
//
// Burton Computer Corporation
// http://www.burton-computer.com
//
// Copyright (c) 2017, Burton Computer Corporation
// All rights reserved.
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//
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// notice, this list of conditions and the following disclaimer in
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package org.javimmutable.collections.util;
import org.javimmutable.collections.Func2;
import org.javimmutable.collections.JImmutableList;
import org.javimmutable.collections.JImmutableListMap;
import org.javimmutable.collections.JImmutableMap;
import org.javimmutable.collections.JImmutableRandomAccessList;
import org.javimmutable.collections.JImmutableSet;
import javax.annotation.Nonnull;
import javax.annotation.concurrent.Immutable;
import java.util.Comparator;
import java.util.Set;
import java.util.function.BiConsumer;
import java.util.function.BinaryOperator;
import java.util.function.Function;
import java.util.function.Supplier;
import java.util.stream.Collector;
import java.util.stream.Collector.Characteristics;
/**
* Utility class providing static methods for collecting various immutable collections using streams.
*/
public class JImmutableCollectors
{
static final Set ORDERED = JImmutables.set(Characteristics.CONCURRENT).getSet();
static final Set UNORDERED = JImmutables.set(Characteristics.UNORDERED, Characteristics.CONCURRENT).getSet();
private JImmutableCollectors()
{
}
/**
* Collects values into a JImmutableList.
*/
@Nonnull
public static Collector> toList()
{
return new CollectorImpl<>(ORDERED,
JImmutables.list(),
(a, v) -> a.insert(v),
(a, b) -> a.insertAll(b));
}
/**
* Collects values into a JImmutableRandomAccessList.
*/
@Nonnull
public static Collector> toRalist()
{
return new CollectorImpl<>(ORDERED,
JImmutables.ralist(),
(a, v) -> a.insert(v),
(a, b) -> a.insertAll(b));
}
/**
* Collects values into a hashed JImmutableSet.
*/
@Nonnull
public static Collector> toSet()
{
return new CollectorImpl<>(UNORDERED,
JImmutables.set(),
(a, v) -> a.insert(v),
(a, b) -> a.insertAll(b));
}
/**
* Collects values into a sorted JImmutableSet using natural sort order of elements.
*/
@Nonnull
public static > Collector> toSortedSet()
{
return new CollectorImpl<>(UNORDERED,
JImmutables.sortedSet(),
(a, v) -> a.insert(v),
(a, b) -> a.insertAll(b));
}
/**
* Collects values into a sorted JImmutableSet using specified Comparator.
*/
@Nonnull
public static Collector> toSortedSet(@Nonnull Comparator comparator)
{
return new CollectorImpl<>(UNORDERED,
JImmutables.sortedSet(comparator),
(a, v) -> a.insert(v),
(a, b) -> a.insertAll(b));
}
/**
* Collects values into a hashed JImmutableListMap using the specified classifier function
* to generate keys from the encountered elements.
*/
@Nonnull
public static Collector> groupingBy(@Nonnull Function classifier)
{
return new CollectorImpl<>(ORDERED,
JImmutables.listMap(),
(a, v) -> a.insert(classifier.apply(v), v),
(a, b) -> combine(a, b));
}
private static JImmutableListMap combine(@Nonnull JImmutableListMap a,
@Nonnull JImmutableListMap b)
{
for (JImmutableMap.Entry> e : b) {
a = a.assign(e.getKey(), a.getList(e.getKey()).insertAll(e.getValue()));
}
return a;
}
private static class Accumulator
{
private Func2 adder;
private Func2 combiner;
private C list;
private Accumulator(@Nonnull Func2 adder,
@Nonnull Func2 combiner,
@Nonnull C list)
{
this.adder = adder;
this.combiner = combiner;
this.list = list;
}
private synchronized void add(T value)
{
list = adder.apply(list, value);
}
private synchronized Accumulator combine(Accumulator other)
{
list = combiner.apply(list, other.list);
return this;
}
}
@Immutable
private static class CollectorImpl
implements Collector, C>
{
private final Set characteristics;
private final C empty;
private final Func2 adder;
private final Func2 combiner;
private CollectorImpl(@Nonnull Set characteristics,
@Nonnull C empty,
@Nonnull Func2 adder,
@Nonnull Func2 combiner)
{
this.characteristics = characteristics;
this.empty = empty;
this.adder = adder;
this.combiner = combiner;
}
@Override
public Supplier> supplier()
{
return () -> new Accumulator<>(adder, combiner, empty);
}
@Override
public BiConsumer, T> accumulator()
{
return (a, v) -> a.add(v);
}
@Override
public BinaryOperator> combiner()
{
return (left, right) -> left.combine(right);
}
@Override
public Function, C> finisher()
{
return a -> a.list;
}
@Override
public Set characteristics()
{
return characteristics;
}
}
}