com.google.common.collect.ImmutableSet Maven / Gradle / Ivy
/*
* 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.collect.ObjectArrays.checkElementNotNull;
import com.google.common.annotations.GwtCompatible;
import com.google.common.annotations.VisibleForTesting;
import com.google.common.primitives.Ints;
import java.io.Serializable;
import java.util.Arrays;
import java.util.Collection;
import java.util.Collections;
import java.util.EnumSet;
import java.util.HashSet;
import java.util.Iterator;
import java.util.Set;
import javax.annotation.Nullable;
/**
* A high-performance, immutable {@code Set} with reliable, user-specified
* iteration order. Does not permit null elements.
*
* Unlike {@link Collections#unmodifiableSet}, which is a view of a
* separate collection that can still change, an instance of this class contains
* its own private data and will never change. This class is convenient
* for {@code public static final} sets ("constant sets") and also lets you
* easily make a "defensive copy" of a set provided to your class by a caller.
*
*
Warning: Like most sets, an {@code ImmutableSet} will not function
* correctly if an element is modified after being placed in the set. For this
* reason, and to avoid general confusion, it is strongly recommended to place
* only immutable objects into this collection.
*
*
This class has been observed to perform significantly better than {@link
* HashSet} for objects with very fast {@link Object#hashCode} implementations
* (as a well-behaved immutable object should). While this class's factory
* methods create hash-based instances, the {@link ImmutableSortedSet} subclass
* performs binary searches instead.
*
*
Note: Although this class is not final, it cannot be subclassed
* outside its package as it has no public or protected constructors. Thus,
* instances of this type are guaranteed to be immutable.
*
*
See the Guava User Guide article on
* immutable collections.
*
* @see ImmutableList
* @see ImmutableMap
* @author Kevin Bourrillion
* @author Nick Kralevich
* @since 2.0 (imported from Google Collections Library)
*/
@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. This set behaves and performs comparably
* to {@link Collections#emptySet}, and is preferable mainly for consistency
* and maintainability of your code.
*/
// Casting to any type is safe because the set will never hold any elements.
@SuppressWarnings({"unchecked"})
public static ImmutableSet of() {
return (ImmutableSet) EmptyImmutableSet.INSTANCE;
}
/**
* Returns an immutable set containing a single element. This set behaves and
* performs comparably to {@link Collections#singleton}, but will not accept
* a null element. It is preferable mainly for consistency and
* maintainability of your code.
*/
public static ImmutableSet of(E element) {
return new SingletonImmutableSet(element);
}
/**
* Returns an immutable set containing the given elements, in order. Repeated
* occurrences of an element (according to {@link Object#equals}) after the
* first are ignored.
*
* @throws NullPointerException if any element is null
*/
public static ImmutableSet of(E e1, E e2) {
return construct(2, e1, e2);
}
/**
* Returns an immutable set containing the given elements, in order. Repeated
* occurrences of an element (according to {@link Object#equals}) after the
* first are ignored.
*
* @throws NullPointerException if any element is null
*/
public static ImmutableSet of(E e1, E e2, E e3) {
return construct(3, e1, e2, e3);
}
/**
* Returns an immutable set containing the given elements, in order. Repeated
* occurrences of an element (according to {@link Object#equals}) after the
* first are ignored.
*
* @throws NullPointerException if any element is null
*/
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, in order. Repeated
* occurrences of an element (according to {@link Object#equals}) after the
* first are ignored.
*
* @throws NullPointerException if any element is null
*/
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, in order. Repeated
* occurrences of an element (according to {@link Object#equals}) after the
* first are ignored.
*
* @throws NullPointerException if any element is null
* @since 3.0 (source-compatible since 2.0)
*/
public static ImmutableSet of(E e1, E e2, E e3, E e4, E e5, E e6,
E... others) {
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:
// 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 (tableSize != chooseTableSize(uniques)) {
// Resize the table when the array includes too many duplicates.
// when this happens, we have already made a copy
return construct(uniques, elements);
} else {
Object[] uniqueElements = (uniques < elements.length)
? ObjectArrays.arraysCopyOf(elements, uniques)
: elements;
return new RegularImmutableSet(uniqueElements, hashCode, table, mask);
}
}
// 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.
*
* Do not call this method with setSize < 2.
*/
@VisibleForTesting static int chooseTableSize(int setSize) {
// 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 the given elements, in order. Repeated
* occurrences of an element (according to {@link Object#equals}) after the
* first are ignored.
*
* @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());
}
}
/**
* Returns an immutable set containing the given elements, in order. Repeated
* occurrences of an element (according to {@link Object#equals}) after the
* first are ignored. This method iterates over {@code elements} at most once.
*
* Note that if {@code s} is a {@code Set}, then {@code
* ImmutableSet.copyOf(s)} returns an {@code ImmutableSet} containing
* each of the strings in {@code s}, while {@code ImmutableSet.of(s)} returns
* a {@code ImmutableSet>} containing one element (the given set
* itself).
*
* Despite the method name, this method attempts to avoid actually copying
* the data when it is safe to do so. The exact circumstances under which a
* copy will or will not be performed are undocumented and subject to change.
*
* @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 the given elements, in order. Repeated
* occurrences of an element (according to {@link Object#equals}) after the
* first are ignored.
*
* @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 the given elements, in order. Repeated
* occurrences of an element (according to {@link Object#equals}) after the
* first are ignored. This method iterates over {@code elements} at most
* once.
*
* Note that if {@code s} is a {@code Set}, then {@code
* ImmutableSet.copyOf(s)} returns an {@code ImmutableSet} containing
* each of the strings in {@code s}, while {@code ImmutableSet.of(s)} returns
* a {@code ImmutableSet>} containing one element (the given set
* itself).
*
* Note: Despite what the method name suggests, {@code copyOf} will
* return constant-space views, rather than linear-space copies, of some
* inputs known to be immutable. For some other immutable inputs, such as key
* sets of an {@code ImmutableMap}, it still performs a copy in order to avoid
* holding references to the values of the map. The heuristics used in this
* decision are undocumented and subject to change except that:
*
* - A full copy will be done of any {@code ImmutableSortedSet}.
* - {@code ImmutableSet.copyOf()} is idempotent with respect to pointer
* equality.
*
*
* This method is safe to use even when {@code elements} is a synchronized
* or concurrent collection that is currently being modified by another
* thread.
*
* @throws NullPointerException if any of {@code elements} is null
* @since 7.0 (source-compatible since 2.0)
*/
public static ImmutableSet copyOf(Collection elements) {
/*
* TODO(user): consider checking for ImmutableAsList here
* TODO(user): consider checking for Multiset here
*/
if (elements instanceof ImmutableSet
&& !(elements instanceof ImmutableSortedSet)) {
@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);
}
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(@Nullable 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();
/*
* 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();
}
/**
* A builder for creating immutable set instances, especially {@code public
* static final} sets ("constant sets"). Example: {@code
*
* public static final ImmutableSet GOOGLE_COLORS =
* new ImmutableSet.Builder()
* .addAll(WEBSAFE_COLORS)
* .add(new Color(0, 191, 255))
* .build();}
*
* Builder instances can be reused; it is safe to call {@link #build} multiple
* times to build multiple sets in series. Each set is a superset of the set
* created before it.
*
* @since 2.0 (imported from Google Collections Library)
*/
public static class Builder extends ImmutableCollection.ArrayBasedBuilder {
/**
* Creates a new builder. The returned builder is equivalent to the builder
* generated by {@link ImmutableSet#builder}.
*/
public Builder() {
this(DEFAULT_INITIAL_CAPACITY);
}
Builder(int capacity) {
super(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
*/
@Override public Builder add(E element) {
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 public Builder add(E... elements) {
super.add(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 {@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
*/
@Override public Builder addAll(Iterable elements) {
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
*/
@Override public Builder addAll(Iterator elements) {
super.addAll(elements);
return this;
}
/**
* Returns a newly-created {@code ImmutableSet} based on the contents of
* the {@code Builder}.
*/
@Override public ImmutableSet build() {
ImmutableSet result = construct(size, contents);
// construct has the side effect of deduping contents, so we update size
// accordingly.
size = result.size();
return result;
}
}
}