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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 static com.google.common.collect.ObjectArrays.checkElementNotNull;
import com.google.common.annotations.Beta;
import com.google.common.annotations.GwtCompatible;
import com.google.common.annotations.VisibleForTesting;
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.util.Arrays;
import java.util.Collection;
import java.util.Collections;
import java.util.Iterator;
import java.util.Set;
import java.util.SortedSet;
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 {
/**
* 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}.
*
* After this method returns, {@code elements} will contain no duplicates, but {@code elements}
* may be the real array backing the returned set, so do not modify it further.
*
*
{@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:
// continue below to handle the general case
}
int tableSize = chooseTableSize(n);
Object[] table = new Object[tableSize];
int mask = tableSize - 1;
int hashCode = 0;
int uniques = 0;
for (int i = 0; i < n; i++) {
Object element = checkElementNotNull(elements[i], i);
int hash = element.hashCode();
for (int j = Hashing.smear(hash); ; j++) {
int index = j & mask;
Object value = table[index];
if (value == null) {
// Came to an empty slot. Put the element here.
elements[uniques++] = element;
table[index] = element;
hashCode += hash;
break;
} else if (value.equals(element)) {
break;
}
}
}
Arrays.fill(elements, uniques, n, null);
if (uniques == 1) {
// There is only one element or elements are all duplicates
@SuppressWarnings("unchecked") // we are careful to only pass in E
E element = (E) elements[0];
return new SingletonImmutableSet(element, hashCode);
} else if (chooseTableSize(uniques) < tableSize / 2) {
// Resize the table when the array includes too many duplicates.
return construct(uniques, elements);
} else {
Object[] uniqueElements =
shouldTrim(uniques, elements.length) ? Arrays.copyOf(elements, uniques) : elements;
return new RegularImmutableSet(uniqueElements, hashCode, table, mask, uniques);
}
}
private static boolean shouldTrim(int actualUnique, int expectedUnique) {
return actualUnique < (expectedUnique >> 1) + (expectedUnique >> 2);
}
// 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;
}
/**
* 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;
}
}
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());
}
}
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 @RetainedWith @NullableDecl private transient ImmutableList asList;
@Override
public ImmutableList asList() {
ImmutableList result = asList;
return (result == null) ? asList = createAsList() : result;
}
ImmutableList createAsList() {
return ImmutableList.asImmutableList(toArray());
}
/*
* 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);
}
/**
* 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.ArrayBasedBuilder {
@NullableDecl @VisibleForTesting Object[] hashTable;
private int hashCode;
/**
* Creates a new builder. The returned builder is equivalent to the builder generated by {@link
* ImmutableSet#builder}.
*/
public Builder() {
super(DEFAULT_INITIAL_CAPACITY);
}
Builder(int capacity) {
super(capacity);
this.hashTable = new Object[chooseTableSize(capacity)];
}
/**
* Adds {@code element} to the {@code ImmutableSet}. If the {@code ImmutableSet} already
* contains {@code element}, then {@code add} has no effect (only the previously added element
* is retained).
*
* @param element the element to add
* @return this {@code Builder} object
* @throws NullPointerException if {@code element} is null
*/
@CanIgnoreReturnValue
@Override
public Builder add(E element) {
checkNotNull(element);
if (hashTable != null && chooseTableSize(size) <= hashTable.length) {
addDeduping(element);
return this;
} else {
hashTable = null;
super.add(element);
return this;
}
}
/**
* 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
*/
@Override
@CanIgnoreReturnValue
public Builder add(E... elements) {
if (hashTable != null) {
for (E e : elements) {
add(e);
}
} else {
super.add(elements);
}
return this;
}
private void addDeduping(E element) {
int mask = hashTable.length - 1;
int hash = element.hashCode();
for (int i = Hashing.smear(hash); ; i++) {
i &= mask;
Object previous = hashTable[i];
if (previous == null) {
hashTable[i] = element;
hashCode += hash;
super.add(element);
return;
} else if (previous.equals(element)) {
return;
}
}
}
/**
* Adds each element of {@code elements} to the {@code ImmutableSet}, ignoring duplicate
* elements (only the first duplicate element is added).
*
* @param elements the {@code Iterable} to add to the {@code ImmutableSet}
* @return this {@code Builder} object
* @throws NullPointerException if {@code elements} is null or contains a null element
*/
@CanIgnoreReturnValue
@Override
public Builder addAll(Iterable elements) {
checkNotNull(elements);
if (hashTable != null) {
for (E e : elements) {
add(e);
}
} else {
super.addAll(elements);
}
return this;
}
/**
* 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 to the {@code ImmutableSet}
* @return this {@code Builder} object
* @throws NullPointerException if {@code elements} is null or contains a null element
*/
@CanIgnoreReturnValue
@Override
public Builder addAll(Iterator elements) {
checkNotNull(elements);
while (elements.hasNext()) {
add(elements.next());
}
return this;
}
@CanIgnoreReturnValue
@SuppressWarnings("unchecked") // ArrayBasedBuilder stores its elements as Object.
Builder combine(Builder other) {
if (hashTable != null) {
for (int i = 0; i < other.size; ++i) {
add((E) other.contents[i]);
}
} else {
addAll(other.contents, other.size);
}
return this;
}
/**
* Returns a newly-created {@code ImmutableSet} based on the contents of the {@code Builder}.
*/
@SuppressWarnings("unchecked")
@Override
public ImmutableSet build() {
switch (size) {
case 0:
return of();
case 1:
return (ImmutableSet) of(contents[0]);
default:
ImmutableSet result;
if (hashTable != null && chooseTableSize(size) == hashTable.length) {
Object[] uniqueElements =
shouldTrim(size, contents.length) ? Arrays.copyOf(contents, size) : contents;
result =
new RegularImmutableSet(
uniqueElements, hashCode, hashTable, hashTable.length - 1, size);
} else {
result = construct(size, contents);
// construct has the side effect of deduping contents, so we update size
// accordingly.
size = result.size();
}
forceCopy = true;
hashTable = null;
return result;
}
}
}
}