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/*
* Copyright (C) 2002-2023 Sebastiano Vigna
*
* 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 it.unimi.dsi.fastutil.objects;
import java.util.Collection;
import java.util.Objects;
import java.util.function.Consumer;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.function.IntFunction;
import java.util.function.Supplier;
import java.util.function.Predicate;
/**
* A class providing static methods and objects that do useful things with type-specific
* collections.
*
* @see java.util.Collections
*/
public final class ObjectCollections {
private ObjectCollections() {
}
/**
* An immutable class representing an empty type-specific collection.
*
*
* This class may be useful to implement your own in case you subclass a type-specific collection.
*/
public abstract static class EmptyCollection extends AbstractObjectCollection {
protected EmptyCollection() {
}
@Override
public boolean contains(Object k) {
return false;
}
@Override
public Object[] toArray() {
return ObjectArrays.EMPTY_ARRAY;
}
@Override
public T[] toArray(T[] array) {
if (array.length > 0) array[0] = null;
return array;
}
@Override
@SuppressWarnings("unchecked")
public ObjectBidirectionalIterator iterator() {
return ObjectIterators.EMPTY_ITERATOR;
}
@Override
@SuppressWarnings("unchecked")
public ObjectSpliterator spliterator() {
return ObjectSpliterators.EMPTY_SPLITERATOR;
}
@Override
public int size() {
return 0;
}
@Override
public void clear() {
}
@Override
public int hashCode() {
return 0;
}
@Override
public boolean equals(Object o) {
if (o == this) return true;
if (!(o instanceof Collection)) return false;
return ((Collection)o).isEmpty();
}
@Override
public void forEach(final Consumer action) {
}
@Override
public boolean containsAll(final Collection c) {
return c.isEmpty();
}
@Override
public boolean addAll(final Collection c) {
throw new UnsupportedOperationException();
}
@Override
public boolean removeAll(final Collection c) {
throw new UnsupportedOperationException();
}
@Override
public boolean retainAll(final Collection c) {
throw new UnsupportedOperationException();
}
@Override
public boolean removeIf(final java.util.function.Predicate filter) {
Objects.requireNonNull(filter);
return false;
}
}
/** A synchronized wrapper class for collections. */
static class SynchronizedCollection implements ObjectCollection, java.io.Serializable {
private static final long serialVersionUID = -7046029254386353129L;
protected final ObjectCollection collection;
protected final Object sync;
protected SynchronizedCollection(final ObjectCollection c, final Object sync) {
this.collection = Objects.requireNonNull(c);
this.sync = sync;
}
protected SynchronizedCollection(final ObjectCollection c) {
this.collection = Objects.requireNonNull(c);
this.sync = this;
}
@Override
public boolean add(final K k) {
synchronized (sync) {
return collection.add(k);
}
}
@Override
public boolean contains(final Object k) {
synchronized (sync) {
return collection.contains(k);
}
}
@Override
public boolean remove(final Object k) {
synchronized (sync) {
return collection.remove(k);
}
}
@Override
public int size() {
synchronized (sync) {
return collection.size();
}
}
@Override
public boolean isEmpty() {
synchronized (sync) {
return collection.isEmpty();
}
}
@Override
public Object[] toArray() {
synchronized (sync) {
return collection.toArray();
}
}
@Override
public T[] toArray(final T[] a) {
synchronized (sync) {
return collection.toArray(a);
}
}
@Override
public ObjectIterator iterator() {
return collection.iterator();
}
@Override
public ObjectSpliterator spliterator() {
return collection.spliterator();
}
@Override
public java.util.stream.Stream stream() {
return collection.stream();
}
@Override
public java.util.stream.Stream parallelStream() {
return collection.parallelStream();
}
@Override
public void forEach(final Consumer action) {
synchronized (sync) {
collection.forEach(action);
}
}
@Override
public boolean addAll(final Collection c) {
synchronized (sync) {
return collection.addAll(c);
}
}
@Override
public boolean containsAll(final Collection c) {
synchronized (sync) {
return collection.containsAll(c);
}
}
@Override
public boolean removeAll(final Collection c) {
synchronized (sync) {
return collection.removeAll(c);
}
}
@Override
public boolean retainAll(final Collection c) {
synchronized (sync) {
return collection.retainAll(c);
}
}
@Override
public boolean removeIf(final Predicate filter) {
synchronized (sync) {
return collection.removeIf(filter);
}
}
@Override
public void clear() {
synchronized (sync) {
collection.clear();
}
}
@Override
public String toString() {
synchronized (sync) {
return collection.toString();
}
}
@Override
public int hashCode() {
synchronized (sync) {
return collection.hashCode();
}
}
@Override
public boolean equals(final Object o) {
if (o == this) return true;
synchronized (sync) {
return collection.equals(o);
}
}
private void writeObject(java.io.ObjectOutputStream s) throws java.io.IOException {
synchronized (sync) {
s.defaultWriteObject();
}
}
}
/**
* Returns a synchronized collection backed by the specified collection.
*
* @param c the collection to be wrapped in a synchronized collection.
* @return a synchronized view of the specified collection.
* @see java.util.Collections#synchronizedCollection(Collection)
*/
public static ObjectCollection synchronize(final ObjectCollection c) {
return new SynchronizedCollection<>(c);
}
/**
* Returns a synchronized collection backed by the specified collection, using an assigned object to
* synchronize.
*
* @param c the collection to be wrapped in a synchronized collection.
* @param sync an object that will be used to synchronize the list access.
* @return a synchronized view of the specified collection.
* @see java.util.Collections#synchronizedCollection(Collection)
*/
public static ObjectCollection synchronize(final ObjectCollection c, final Object sync) {
return new SynchronizedCollection<>(c, sync);
}
/** An unmodifiable wrapper class for collections. */
static class UnmodifiableCollection implements ObjectCollection, java.io.Serializable {
private static final long serialVersionUID = -7046029254386353129L;
protected final ObjectCollection collection;
protected UnmodifiableCollection(final ObjectCollection c) {
this.collection = Objects.requireNonNull(c);
}
@Override
public boolean add(final K k) {
throw new UnsupportedOperationException();
}
@Override
public boolean remove(final Object k) {
throw new UnsupportedOperationException();
}
@Override
public int size() {
return collection.size();
}
@Override
public boolean isEmpty() {
return collection.isEmpty();
}
@Override
public boolean contains(final Object o) {
return collection.contains(o);
}
@Override
public ObjectIterator iterator() {
return ObjectIterators.unmodifiable(collection.iterator());
}
@Override
@SuppressWarnings("unchecked")
public ObjectSpliterator spliterator() {
return (ObjectSpliterator)collection.spliterator();
}
@Override
@SuppressWarnings("unchecked")
public java.util.stream.Stream stream() {
return (java.util.stream.Stream)collection.stream();
}
@Override
@SuppressWarnings("unchecked")
public java.util.stream.Stream parallelStream() {
return (java.util.stream.Stream)collection.parallelStream();
}
@Override
public void clear() {
throw new UnsupportedOperationException();
}
@Override
public T[] toArray(final T[] a) {
return collection.toArray(a);
}
@Override
public Object[] toArray() {
return collection.toArray();
}
@Override
public void forEach(final Consumer action) {
collection.forEach(action);
}
@Override
public boolean containsAll(Collection c) {
return collection.containsAll(c);
}
@Override
public boolean addAll(Collection c) {
throw new UnsupportedOperationException();
}
@Override
public boolean removeAll(Collection c) {
throw new UnsupportedOperationException();
}
@Override
public boolean retainAll(Collection c) {
throw new UnsupportedOperationException();
}
@Override
public boolean removeIf(final Predicate filter) {
throw new UnsupportedOperationException();
}
@Override
public String toString() {
return collection.toString();
}
@Override
public int hashCode() {
return collection.hashCode();
}
@Override
public boolean equals(final Object o) {
if (o == this) return true;
return collection.equals(o);
}
}
/**
* Returns an unmodifiable collection backed by the specified collection.
*
* @param c the collection to be wrapped in an unmodifiable collection.
* @return an unmodifiable view of the specified collection.
* @see java.util.Collections#unmodifiableCollection(Collection)
*/
public static ObjectCollection unmodifiable(final ObjectCollection c) {
return new UnmodifiableCollection<>(c);
}
/** A collection wrapper class for iterables. */
public static class IterableCollection extends AbstractObjectCollection implements java.io.Serializable {
private static final long serialVersionUID = -7046029254386353129L;
protected final ObjectIterable iterable;
protected IterableCollection(final ObjectIterable iterable) {
this.iterable = Objects.requireNonNull(iterable);
}
@Override
public int size() {
long size = iterable.spliterator().getExactSizeIfKnown();
if (size >= 0) return (int)Math.min(Integer.MAX_VALUE, size);
int c = 0;
final ObjectIterator iterator = iterator();
while (iterator.hasNext()) {
iterator.next();
c++;
}
return c;
}
@Override
public boolean isEmpty() {
return !iterable.iterator().hasNext();
}
@Override
public ObjectIterator iterator() {
return iterable.iterator();
}
@Override
public ObjectSpliterator spliterator() {
return iterable.spliterator();
}
}
/**
* Returns an unmodifiable collection backed by the specified iterable.
*
* @param iterable the iterable object to be wrapped in an unmodifiable collection.
* @return an unmodifiable collection view of the specified iterable.
*/
public static ObjectCollection asCollection(final ObjectIterable iterable) {
if (iterable instanceof ObjectCollection) return (ObjectCollection)iterable;
// TODO test for Collection but not our collection, and make a wrapper for it.
return new IterableCollection<>(iterable);
}
/**
* Helper class for size decreasing size estimation.
*
*
* Used to implement {@code toXWithExpectedSize} to prevent allocating a data structure big enough
* for the full stream in every thread, when only one thread (typically the first one) is going to
* need to "see" all of it at some point.
*
*
* Currently set to always assume a roughly split-by-two strategy from the
* {@link java.util.Spliterator} backing the {@link java.util.stream.Stream} (or primitive
* equivalent). This may perform worse for {@code Spliterator}s that don't (for example the ones
* that wrap an {@link java.util.Iterator} as a {@code Spliterator}). This is quite rare in practice
* however. But note that even in such cases, this would still perform no worse (modulo
* some trivial amount) then the default "flat size for every list" method of combining. A way to
* detect such cases and use a different size estimation strategy may come in the future.
*
*
* See the {@linkplain #SizeDecreasingSupplier constructor} for requirements of the {@link #builder}
* functor.
*/
static class SizeDecreasingSupplier> implements Supplier {
static final int RECOMMENDED_MIN_SIZE = 8;
final AtomicInteger suppliedCount = new AtomicInteger(0);
final int expectedFinalSize;
final IntFunction builder;
/**
* Construct this {@link SizeDecreasingSupplier}.
*
* @param expectedFinalSize The expected size of the entire remaining contents of the {@code Stream}
* and thus what size the Collection holding the final results should try to be
* preallocated to.
* @param builder the builder function.
*
* The input integer will be the size of the collection to preallocate.
*
* It is recommended that you allocate a minimum size if the given {@code size} is small.
* {@link #RECOMMENDED_MIN_SIZE} gives a good enough ballpark for most cases.
*
* The subclass is free to use the default constructor for the Collection construction
* instead of the {@code size} given if {@code size} falls below the default size used
* for the default initial capacity for that Collection implementation. Often such
* default constructors contain additional optimizations that giving an explicit initial
* capacity would not do (even if given the default capacity as the initial capacity
* explicitly).
*
* {@link Supplier#get() get()} of the {@link IntFunction} must return non-{@code null}.
*/
SizeDecreasingSupplier(int expectedFinalSize, IntFunction builder) {
this.expectedFinalSize = expectedFinalSize;
this.builder = builder;
}
// This method may be worth pulling into a shared superclass.
@Override
public C get() {
// The "correct" splitting (assuming split by two) would be
// expectedFinalSize / floor(ln_2(++suppliedCount)). But that seems too much trouble to be worth it.
// Instead we will take a simple harmonically decreasing ratio (1, 1/2, 1/3, 1/4)
//
// Round up int math (to round up, not down) adapted from https://stackoverflow.com/a/503201.
int expectedNeededNextSize = 1 + ((expectedFinalSize - 1) / suppliedCount.incrementAndGet());
if (expectedNeededNextSize < 0) {
// Overflow (and weird below zero results) failsafe
expectedNeededNextSize = RECOMMENDED_MIN_SIZE;
}
return builder.apply(expectedNeededNextSize);
}
}
}