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/*
* Copyright (C) 2007 The Guava Authors
*
* 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 com.google.common.collect;
import static com.google.common.base.Preconditions.checkArgument;
import static com.google.common.base.Preconditions.checkNotNull;
import static com.google.common.collect.CollectPreconditions.checkNonnegative;
import com.google.common.annotations.Beta;
import com.google.common.annotations.GwtCompatible;
import com.google.common.annotations.VisibleForTesting;
import com.google.common.math.IntMath;
import com.google.common.primitives.Ints;
import com.google.errorprone.annotations.CanIgnoreReturnValue;
import com.google.errorprone.annotations.concurrent.LazyInit;
import com.google.j2objc.annotations.RetainedWith;
import java.io.Serializable;
import java.math.RoundingMode;
import java.util.Arrays;
import java.util.Collection;
import java.util.Collections;
import java.util.EnumSet;
import java.util.Iterator;
import java.util.Set;
import java.util.SortedSet;
import java.util.Spliterator;
import java.util.function.Consumer;
import java.util.stream.Collector;
import org.checkerframework.checker.nullness.compatqual.NullableDecl;
/**
* A {@link Set} whose contents will never change, with many other important properties detailed at
* {@link ImmutableCollection}.
*
* @since 2.0
*/
@GwtCompatible(serializable = true, emulated = true)
@SuppressWarnings("serial") // we're overriding default serialization
public abstract class ImmutableSet extends ImmutableCollection implements Set {
static final int SPLITERATOR_CHARACTERISTICS =
ImmutableCollection.SPLITERATOR_CHARACTERISTICS | Spliterator.DISTINCT;
/**
* Returns a {@code Collector} that accumulates the input elements into a new {@code
* ImmutableSet}. Elements appear in the resulting set in the encounter order of the stream; if
* the stream contains duplicates (according to {@link Object#equals(Object)}), only the first
* duplicate in encounter order will appear in the result.
*
* @since 21.0
*/
@Beta
public static Collector> toImmutableSet() {
return CollectCollectors.toImmutableSet();
}
/**
* Returns the empty immutable set. Preferred over {@link Collections#emptySet} for code
* consistency, and because the return type conveys the immutability guarantee.
*/
@SuppressWarnings({"unchecked"}) // fully variant implementation (never actually produces any Es)
public static ImmutableSet of() {
return (ImmutableSet) RegularImmutableSet.EMPTY;
}
/**
* Returns an immutable set containing {@code element}. Preferred over {@link
* Collections#singleton} for code consistency, {@code null} rejection, and because the return
* type conveys the immutability guarantee.
*/
public static ImmutableSet of(E element) {
return new SingletonImmutableSet(element);
}
/**
* Returns an immutable set containing the given elements, minus duplicates, in the order each was
* first specified. That is, if multiple elements are {@linkplain Object#equals equal}, all except
* the first are ignored.
*/
public static ImmutableSet of(E e1, E e2) {
return construct(2, e1, e2);
}
/**
* Returns an immutable set containing the given elements, minus duplicates, in the order each was
* first specified. That is, if multiple elements are {@linkplain Object#equals equal}, all except
* the first are ignored.
*/
public static ImmutableSet of(E e1, E e2, E e3) {
return construct(3, e1, e2, e3);
}
/**
* Returns an immutable set containing the given elements, minus duplicates, in the order each was
* first specified. That is, if multiple elements are {@linkplain Object#equals equal}, all except
* the first are ignored.
*/
public static ImmutableSet of(E e1, E e2, E e3, E e4) {
return construct(4, e1, e2, e3, e4);
}
/**
* Returns an immutable set containing the given elements, minus duplicates, in the order each was
* first specified. That is, if multiple elements are {@linkplain Object#equals equal}, all except
* the first are ignored.
*/
public static ImmutableSet of(E e1, E e2, E e3, E e4, E e5) {
return construct(5, e1, e2, e3, e4, e5);
}
/**
* Returns an immutable set containing the given elements, minus duplicates, in the order each was
* first specified. That is, if multiple elements are {@linkplain Object#equals equal}, all except
* the first are ignored.
*
* The array {@code others} must not be longer than {@code Integer.MAX_VALUE - 6}.
*
* @since 3.0 (source-compatible since 2.0)
*/
@SafeVarargs // For Eclipse. For internal javac we have disabled this pointless type of warning.
public static ImmutableSet of(E e1, E e2, E e3, E e4, E e5, E e6, E... others) {
checkArgument(
others.length <= Integer.MAX_VALUE - 6,
"the total number of elements must fit in an int");
final int paramCount = 6;
Object[] elements = new Object[paramCount + others.length];
elements[0] = e1;
elements[1] = e2;
elements[2] = e3;
elements[3] = e4;
elements[4] = e5;
elements[5] = e6;
System.arraycopy(others, 0, elements, paramCount, others.length);
return construct(elements.length, elements);
}
/**
* Constructs an {@code ImmutableSet} from the first {@code n} elements of the specified array. If
* {@code k} is the size of the returned {@code ImmutableSet}, then the unique elements of {@code
* elements} will be in the first {@code k} positions, and {@code elements[i] == null} for {@code
* k <= i < n}.
*
* This may modify {@code elements}. Additionally, if {@code n == elements.length} and {@code
* elements} contains no duplicates, {@code elements} may be used without copying in the returned
* {@code ImmutableSet}, in which case it may no longer be modified.
*
*
{@code elements} may contain only values of type {@code E}.
*
* @throws NullPointerException if any of the first {@code n} elements of {@code elements} is null
*/
private static ImmutableSet construct(int n, Object... elements) {
switch (n) {
case 0:
return of();
case 1:
@SuppressWarnings("unchecked") // safe; elements contains only E's
E elem = (E) elements[0];
return of(elem);
default:
SetBuilderImpl builder =
new RegularSetBuilderImpl(ImmutableCollection.Builder.DEFAULT_INITIAL_CAPACITY);
for (int i = 0; i < n; i++) {
@SuppressWarnings("unchecked")
E e = (E) checkNotNull(elements[i]);
builder = builder.add(e);
}
return builder.review().build();
}
}
/**
* Returns an immutable set containing each of {@code elements}, minus duplicates, in the order
* each appears first in the source collection.
*
* Performance note: This method will sometimes recognize that the actual copy operation
* is unnecessary; for example, {@code copyOf(copyOf(anArrayList))} will copy the data only once.
* This reduces the expense of habitually making defensive copies at API boundaries. However, the
* precise conditions for skipping the copy operation are undefined.
*
* @throws NullPointerException if any of {@code elements} is null
* @since 7.0 (source-compatible since 2.0)
*/
public static ImmutableSet copyOf(Collection elements) {
/*
* TODO(lowasser): consider checking for ImmutableAsList here
* TODO(lowasser): consider checking for Multiset here
*/
// Don't refer to ImmutableSortedSet by name so it won't pull in all that code
if (elements instanceof ImmutableSet && !(elements instanceof SortedSet)) {
@SuppressWarnings("unchecked") // all supported methods are covariant
ImmutableSet set = (ImmutableSet) elements;
if (!set.isPartialView()) {
return set;
}
} else if (elements instanceof EnumSet) {
return copyOfEnumSet((EnumSet) elements);
}
Object[] array = elements.toArray();
return construct(array.length, array);
}
/**
* Returns an immutable set containing each of {@code elements}, minus duplicates, in the order
* each appears first in the source iterable. This method iterates over {@code elements} only
* once.
*
* Performance note: This method will sometimes recognize that the actual copy operation
* is unnecessary; for example, {@code copyOf(copyOf(anArrayList))} should copy the data only
* once. This reduces the expense of habitually making defensive copies at API boundaries.
* However, the precise conditions for skipping the copy operation are undefined.
*
* @throws NullPointerException if any of {@code elements} is null
*/
public static ImmutableSet copyOf(Iterable elements) {
return (elements instanceof Collection)
? copyOf((Collection) elements)
: copyOf(elements.iterator());
}
/**
* Returns an immutable set containing each of {@code elements}, minus duplicates, in the order
* each appears first in the source iterator.
*
* @throws NullPointerException if any of {@code elements} is null
*/
public static ImmutableSet copyOf(Iterator elements) {
// We special-case for 0 or 1 elements, but anything further is madness.
if (!elements.hasNext()) {
return of();
}
E first = elements.next();
if (!elements.hasNext()) {
return of(first);
} else {
return new ImmutableSet.Builder().add(first).addAll(elements).build();
}
}
/**
* Returns an immutable set containing each of {@code elements}, minus duplicates, in the order
* each appears first in the source array.
*
* @throws NullPointerException if any of {@code elements} is null
* @since 3.0
*/
public static ImmutableSet copyOf(E[] elements) {
switch (elements.length) {
case 0:
return of();
case 1:
return of(elements[0]);
default:
return construct(elements.length, elements.clone());
}
}
@SuppressWarnings("rawtypes") // necessary to compile against Java 8
private static ImmutableSet copyOfEnumSet(EnumSet enumSet) {
return ImmutableEnumSet.asImmutable(EnumSet.copyOf(enumSet));
}
ImmutableSet() {}
/** Returns {@code true} if the {@code hashCode()} method runs quickly. */
boolean isHashCodeFast() {
return false;
}
@Override
public boolean equals(@NullableDecl Object object) {
if (object == this) {
return true;
} else if (object instanceof ImmutableSet
&& isHashCodeFast()
&& ((ImmutableSet) object).isHashCodeFast()
&& hashCode() != object.hashCode()) {
return false;
}
return Sets.equalsImpl(this, object);
}
@Override
public int hashCode() {
return Sets.hashCodeImpl(this);
}
// This declaration is needed to make Set.iterator() and
// ImmutableCollection.iterator() consistent.
@Override
public abstract UnmodifiableIterator iterator();
@LazyInit @NullableDecl @RetainedWith private transient ImmutableList asList;
@Override
public ImmutableList asList() {
ImmutableList result = asList;
return (result == null) ? asList = createAsList() : result;
}
ImmutableList createAsList() {
return new RegularImmutableAsList(this, toArray());
}
abstract static class Indexed extends ImmutableSet {
abstract E get(int index);
@Override
public UnmodifiableIterator iterator() {
return asList().iterator();
}
@Override
public Spliterator spliterator() {
return CollectSpliterators.indexed(size(), SPLITERATOR_CHARACTERISTICS, this::get);
}
@Override
public void forEach(Consumer consumer) {
checkNotNull(consumer);
int n = size();
for (int i = 0; i < n; i++) {
consumer.accept(get(i));
}
}
@Override
int copyIntoArray(Object[] dst, int offset) {
return asList().copyIntoArray(dst, offset);
}
@Override
ImmutableList createAsList() {
return new ImmutableAsList() {
@Override
public E get(int index) {
return Indexed.this.get(index);
}
@Override
Indexed delegateCollection() {
return Indexed.this;
}
};
}
}
/*
* This class is used to serialize all ImmutableSet instances, except for
* ImmutableEnumSet/ImmutableSortedSet, regardless of implementation type. It
* captures their "logical contents" and they are reconstructed using public
* static factories. This is necessary to ensure that the existence of a
* particular implementation type is an implementation detail.
*/
private static class SerializedForm implements Serializable {
final Object[] elements;
SerializedForm(Object[] elements) {
this.elements = elements;
}
Object readResolve() {
return copyOf(elements);
}
private static final long serialVersionUID = 0;
}
@Override
Object writeReplace() {
return new SerializedForm(toArray());
}
/**
* Returns a new builder. The generated builder is equivalent to the builder created by the {@link
* Builder} constructor.
*/
public static Builder builder() {
return new Builder();
}
/**
* Returns a new builder, expecting the specified number of distinct elements to be added.
*
* If {@code expectedSize} is exactly the number of distinct elements added to the builder
* before {@link Builder#build} is called, the builder is likely to perform better than an unsized
* {@link #builder()} would have.
*
*
It is not specified if any performance benefits apply if {@code expectedSize} is close to,
* but not exactly, the number of distinct elements added to the builder.
*
* @since 23.1
*/
@Beta
public static Builder builderWithExpectedSize(int expectedSize) {
checkNonnegative(expectedSize, "expectedSize");
return new Builder(expectedSize);
}
/** Builds a new open-addressed hash table from the first n objects in elements. */
static Object[] rebuildHashTable(int newTableSize, Object[] elements, int n) {
Object[] hashTable = new Object[newTableSize];
int mask = hashTable.length - 1;
for (int i = 0; i < n; i++) {
Object e = elements[i];
int j0 = Hashing.smear(e.hashCode());
for (int j = j0; ; j++) {
int index = j & mask;
if (hashTable[index] == null) {
hashTable[index] = e;
break;
}
}
}
return hashTable;
}
/**
* A builder for creating {@code ImmutableSet} instances. Example:
*
* {@code
* static final ImmutableSet GOOGLE_COLORS =
* ImmutableSet.builder()
* .addAll(WEBSAFE_COLORS)
* .add(new Color(0, 191, 255))
* .build();
* }
*
* Elements appear in the resulting set in the same order they were first added to the builder.
*
*
Building does not change the state of the builder, so it is still possible to add more
* elements and to build again.
*
* @since 2.0
*/
public static class Builder extends ImmutableCollection.Builder {
private SetBuilderImpl impl;
boolean forceCopy;
public Builder() {
this(DEFAULT_INITIAL_CAPACITY);
}
Builder(int capacity) {
impl = new RegularSetBuilderImpl(capacity);
}
Builder(@SuppressWarnings("unused") boolean subclass) {
this.impl = null; // unused
}
@VisibleForTesting
void forceJdk() {
this.impl = new JdkBackedSetBuilderImpl(impl);
}
final void copyIfNecessary() {
if (forceCopy) {
copy();
forceCopy = false;
}
}
void copy() {
impl = impl.copy();
}
@Override
@CanIgnoreReturnValue
public Builder add(E element) {
checkNotNull(element);
copyIfNecessary();
impl = impl.add(element);
return this;
}
@Override
@CanIgnoreReturnValue
public Builder add(E... elements) {
super.add(elements);
return this;
}
@Override
/**
* Adds each element of {@code elements} to the {@code ImmutableSet}, ignoring duplicate
* elements (only the first duplicate element is added).
*
* @param elements the elements to add
* @return this {@code Builder} object
* @throws NullPointerException if {@code elements} is null or contains a null element
*/
@CanIgnoreReturnValue
public Builder addAll(Iterable elements) {
super.addAll(elements);
return this;
}
@Override
@CanIgnoreReturnValue
public Builder addAll(Iterator elements) {
super.addAll(elements);
return this;
}
Builder combine(Builder other) {
copyIfNecessary();
this.impl = this.impl.combine(other.impl);
return this;
}
@Override
public ImmutableSet build() {
forceCopy = true;
impl = impl.review();
return impl.build();
}
}
/** Swappable internal implementation of an ImmutableSet.Builder. */
private abstract static class SetBuilderImpl {
E[] dedupedElements;
int distinct;
@SuppressWarnings("unchecked")
SetBuilderImpl(int expectedCapacity) {
this.dedupedElements = (E[]) new Object[expectedCapacity];
this.distinct = 0;
}
/** Initializes this SetBuilderImpl with a copy of the deduped elements array from toCopy. */
SetBuilderImpl(SetBuilderImpl toCopy) {
this.dedupedElements = Arrays.copyOf(toCopy.dedupedElements, toCopy.dedupedElements.length);
this.distinct = toCopy.distinct;
}
/**
* Resizes internal data structures if necessary to store the specified number of distinct
* elements.
*/
private void ensureCapacity(int minCapacity) {
if (minCapacity > dedupedElements.length) {
int newCapacity =
ImmutableCollection.Builder.expandedCapacity(dedupedElements.length, minCapacity);
dedupedElements = Arrays.copyOf(dedupedElements, newCapacity);
}
}
/** Adds e to the insertion-order array of deduplicated elements. Calls ensureCapacity. */
final void addDedupedElement(E e) {
ensureCapacity(distinct + 1);
dedupedElements[distinct++] = e;
}
/**
* Adds e to this SetBuilderImpl, returning the updated result. Only use the returned
* SetBuilderImpl, since we may switch implementations if e.g. hash flooding is detected.
*/
abstract SetBuilderImpl add(E e);
/** Adds all the elements from the specified SetBuilderImpl to this SetBuilderImpl. */
final SetBuilderImpl combine(SetBuilderImpl other) {
SetBuilderImpl result = this;
for (int i = 0; i < other.distinct; i++) {
result = result.add(other.dedupedElements[i]);
}
return result;
}
/**
* Creates a new copy of this SetBuilderImpl. Modifications to that SetBuilderImpl will not
* affect this SetBuilderImpl or sets constructed from this SetBuilderImpl via build().
*/
abstract SetBuilderImpl copy();
/**
* Call this before build(). Does a final check on the internal data structures, e.g. shrinking
* unnecessarily large structures or detecting previously unnoticed hash flooding.
*/
SetBuilderImpl review() {
return this;
}
abstract ImmutableSet build();
}
// We use power-of-2 tables, and this is the highest int that's a power of 2
static final int MAX_TABLE_SIZE = Ints.MAX_POWER_OF_TWO;
// Represents how tightly we can pack things, as a maximum.
private static final double DESIRED_LOAD_FACTOR = 0.7;
// If the set has this many elements, it will "max out" the table size
private static final int CUTOFF = (int) (MAX_TABLE_SIZE * DESIRED_LOAD_FACTOR);
/**
* Returns an array size suitable for the backing array of a hash table that uses open addressing
* with linear probing in its implementation. The returned size is the smallest power of two that
* can hold setSize elements with the desired load factor. Always returns at least setSize + 2.
*/
@VisibleForTesting
static int chooseTableSize(int setSize) {
setSize = Math.max(setSize, 2);
// Correct the size for open addressing to match desired load factor.
if (setSize < CUTOFF) {
// Round up to the next highest power of 2.
int tableSize = Integer.highestOneBit(setSize - 1) << 1;
while (tableSize * DESIRED_LOAD_FACTOR < setSize) {
tableSize <<= 1;
}
return tableSize;
}
// The table can't be completely full or we'll get infinite reprobes
checkArgument(setSize < MAX_TABLE_SIZE, "collection too large");
return MAX_TABLE_SIZE;
}
/**
* We attempt to detect deliberate hash flooding attempts, and if one is detected, fall back to a
* wrapper around j.u.HashSet, which has built in flooding protection. HASH_FLOODING_FPP is the
* maximum allowed probability of falsely detecting a hash flooding attack if the input is
* randomly generated.
*
* MAX_RUN_MULTIPLIER was determined experimentally to match this FPP.
*/
static final double HASH_FLOODING_FPP = 0.001;
// NB: yes, this is surprisingly high, but that's what the experiments said was necessary
static final int MAX_RUN_MULTIPLIER = 12;
/**
* Checks the whole hash table for poor hash distribution. Takes O(n).
*
*
The online hash flooding detecting in RegularSetBuilderImpl.add can detect e.g. many exactly
* matching hash codes, which would cause construction to take O(n^2), but can't detect e.g. hash
* codes adversarially designed to go into ascending table locations, which keeps construction
* O(n) (as desired) but then can have O(n) queries later.
*
*
If this returns false, then no query can take more than O(log n).
*
*
Note that for a RegularImmutableSet with elements with truly random hash codes, contains
* operations take expected O(1) time but with high probability take O(log n) for at least some
* element. (https://en.wikipedia.org/wiki/Linear_probing#Analysis)
*/
static boolean hashFloodingDetected(Object[] hashTable) {
int maxRunBeforeFallback = maxRunBeforeFallback(hashTable.length);
// Test for a run wrapping around the end of the table, then check for runs in the middle.
int endOfStartRun;
for (endOfStartRun = 0; endOfStartRun < hashTable.length; ) {
if (hashTable[endOfStartRun] == null) {
break;
}
endOfStartRun++;
if (endOfStartRun > maxRunBeforeFallback) {
return true;
}
}
int startOfEndRun;
for (startOfEndRun = hashTable.length - 1; startOfEndRun > endOfStartRun; startOfEndRun--) {
if (hashTable[startOfEndRun] == null) {
break;
}
if (endOfStartRun + (hashTable.length - 1 - startOfEndRun) > maxRunBeforeFallback) {
return true;
}
}
for (int i = endOfStartRun + 1; i < startOfEndRun; i++) {
for (int runLength = 0; i < startOfEndRun && hashTable[i] != null; i++) {
runLength++;
if (runLength > maxRunBeforeFallback) {
return true;
}
}
}
return false;
}
/**
* If more than this many consecutive positions are filled in a table of the specified size,
* report probable hash flooding.
*/
static int maxRunBeforeFallback(int tableSize) {
return MAX_RUN_MULTIPLIER * IntMath.log2(tableSize, RoundingMode.UNNECESSARY);
}
/**
* Default implementation of the guts of ImmutableSet.Builder, creating an open-addressed hash
* table and deduplicating elements as they come, so it only allocates O(max(distinct,
* expectedCapacity)) rather than O(calls to add).
*
*
This implementation attempts to detect hash flooding, and if it's identified, falls back to
* JdkBackedSetBuilderImpl.
*/
private static final class RegularSetBuilderImpl extends SetBuilderImpl {
private Object[] hashTable;
private int maxRunBeforeFallback;
private int expandTableThreshold;
private int hashCode;
RegularSetBuilderImpl(int expectedCapacity) {
super(expectedCapacity);
int tableSize = chooseTableSize(expectedCapacity);
this.hashTable = new Object[tableSize];
this.maxRunBeforeFallback = maxRunBeforeFallback(tableSize);
this.expandTableThreshold = (int) (DESIRED_LOAD_FACTOR * tableSize);
}
RegularSetBuilderImpl(RegularSetBuilderImpl toCopy) {
super(toCopy);
this.hashTable = Arrays.copyOf(toCopy.hashTable, toCopy.hashTable.length);
this.maxRunBeforeFallback = toCopy.maxRunBeforeFallback;
this.expandTableThreshold = toCopy.expandTableThreshold;
this.hashCode = toCopy.hashCode;
}
void ensureTableCapacity(int minCapacity) {
if (minCapacity > expandTableThreshold && hashTable.length < MAX_TABLE_SIZE) {
int newTableSize = hashTable.length * 2;
hashTable = rebuildHashTable(newTableSize, dedupedElements, distinct);
maxRunBeforeFallback = maxRunBeforeFallback(newTableSize);
expandTableThreshold = (int) (DESIRED_LOAD_FACTOR * newTableSize);
}
}
@Override
SetBuilderImpl add(E e) {
checkNotNull(e);
int eHash = e.hashCode();
int i0 = Hashing.smear(eHash);
int mask = hashTable.length - 1;
for (int i = i0; i - i0 < maxRunBeforeFallback; i++) {
int index = i & mask;
Object tableEntry = hashTable[index];
if (tableEntry == null) {
addDedupedElement(e);
hashTable[index] = e;
hashCode += eHash;
ensureTableCapacity(distinct); // rebuilds table if necessary
return this;
} else if (tableEntry.equals(e)) { // not a new element, ignore
return this;
}
}
// we fell out of the loop due to a long run; fall back to JDK impl
return new JdkBackedSetBuilderImpl(this).add(e);
}
@Override
SetBuilderImpl copy() {
return new RegularSetBuilderImpl(this);
}
@Override
SetBuilderImpl review() {
int targetTableSize = chooseTableSize(distinct);
if (targetTableSize * 2 < hashTable.length) {
hashTable = rebuildHashTable(targetTableSize, dedupedElements, distinct);
}
return hashFloodingDetected(hashTable) ? new JdkBackedSetBuilderImpl(this) : this;
}
@Override
ImmutableSet build() {
switch (distinct) {
case 0:
return of();
case 1:
return of(dedupedElements[0]);
default:
Object[] elements =
(distinct == dedupedElements.length)
? dedupedElements
: Arrays.copyOf(dedupedElements, distinct);
return new RegularImmutableSet(elements, hashCode, hashTable, hashTable.length - 1);
}
}
}
/**
* SetBuilderImpl version that uses a JDK HashSet, which has built in hash flooding protection.
*/
private static final class JdkBackedSetBuilderImpl extends SetBuilderImpl {
private final Set