com.google.common.collect.ImmutableSet Maven / Gradle / Ivy
/*
* Copyright (C) 2007 Google Inc.
*
* 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.checkNotNull;
import com.google.common.annotations.GwtCompatible;
import java.io.Serializable;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
import java.util.Collections;
import java.util.HashSet;
import java.util.Iterator;
import java.util.List;
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 ImmutableList
* @see ImmutableMap
* @author Kevin Bourrillion
* @author Nick Kralevich
* @since 2 (imported from Google Collections Library)
*/
// TODO: benchmark and optimize all creation paths, which are a mess right now
@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
*/
@SuppressWarnings("unchecked")
public static ImmutableSet of(E e1, E e2) {
return create(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
*/
@SuppressWarnings("unchecked")
public static ImmutableSet of(E e1, E e2, E e3) {
return create(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
*/
@SuppressWarnings("unchecked")
public static ImmutableSet of(E e1, E e2, E e3, E e4) {
return create(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
*/
@SuppressWarnings("unchecked")
public static ImmutableSet of(E e1, E e2, E e3, E e4, E e5) {
return create(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 (source-compatible since release 2)
*/
@SuppressWarnings("unchecked")
public static ImmutableSet of(E e1, E e2, E e3, E e4, E e5, E e6,
E... others) {
int size = others.length + 6;
List all = new ArrayList(size);
Collections.addAll(all, e1, e2, e3, e4, e5, e6);
Collections.addAll(all, others);
return create(all, 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.
*
* @deprecated use {@link #copyOf(Object[])}.
* @throws NullPointerException if any of {@code elements} is null
* @since 2 (changed from varargs in release 3)
*/
// TODO: when this is removed, remember to remove from ISS and ISSFS too
@Deprecated
public static ImmutableSet of(E[] elements) {
return copyOf(elements);
}
/**
* 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
*/
public static ImmutableSet copyOf(E[] elements) {
switch (elements.length) {
case 0:
return of();
case 1:
return of(elements[0]);
default:
return create(elements);
}
}
/**
* 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, if {@code elements}
* is an {@code ImmutableSet} (but not an {@code ImmutableSortedSet}), no copy
* will actually be performed, and the given set itself will be returned.
*
* @throws NullPointerException if any of {@code elements} is null
*/
public static ImmutableSet copyOf(Iterable elements) {
if (elements instanceof ImmutableSet
&& !(elements instanceof ImmutableSortedSet)) {
@SuppressWarnings("unchecked") // all supported methods are covariant
ImmutableSet set = (ImmutableSet) elements;
return set;
}
return copyOfInternal(Collections2.toCollection(elements));
}
/**
* 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) {
Collection list = Lists.newArrayList(elements);
return copyOfInternal(list);
}
private static ImmutableSet copyOfInternal(
Collection collection) {
// TODO: Support concurrent collections that change while this method is
// running.
switch (collection.size()) {
case 0:
return of();
case 1:
// TODO: Remove "ImmutableSet." when eclipse bug is fixed.
return ImmutableSet.of(collection.iterator().next());
default:
return create(collection, collection.size());
}
}
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;
}
if (object instanceof ImmutableSet
&& isHashCodeFast()
&& ((ImmutableSet) object).isHashCodeFast()
&& hashCode() != object.hashCode()) {
return false;
}
return Collections2.setEquals(this, object);
}
@Override public int hashCode() {
int hashCode = 0;
for (Object o : this) {
hashCode += o.hashCode();
}
return hashCode;
}
// This declaration is needed to make Set.iterator() and
// ImmutableCollection.iterator() consistent.
@Override public abstract UnmodifiableIterator iterator();
private static ImmutableSet create(E... elements) {
return create(Arrays.asList(elements), elements.length);
}
private static ImmutableSet create(
Iterable iterable, int count) {
// count is always the (nonzero) number of elements in the iterable
int tableSize = Hashing.chooseTableSize(count);
Object[] table = new Object[tableSize];
int mask = tableSize - 1;
List elements = new ArrayList(count);
int hashCode = 0;
for (E element : iterable) {
int hash = element.hashCode();
for (int i = Hashing.smear(hash); true; i++) {
int index = i & mask;
Object value = table[index];
if (value == null) {
// Came to an empty bucket. Put the element here.
table[index] = element;
elements.add(element);
hashCode += hash;
break;
} else if (value.equals(element)) {
break; // Found a duplicate. Nothing to do.
}
}
}
if (elements.size() == 1) {
// The iterable contained only duplicates of the same element.
return new SingletonImmutableSet(elements.get(0), hashCode);
} else if (tableSize > Hashing.chooseTableSize(elements.size())) {
// Resize the table when the iterable includes too many duplicates.
return create(elements, elements.size());
} else {
return new RegularImmutableSet(
elements.toArray(), hashCode, table, mask);
}
}
abstract static class ArrayImmutableSet extends ImmutableSet {
// the elements (two or more) in the desired order.
final transient Object[] elements;
ArrayImmutableSet(Object[] elements) {
this.elements = elements;
}
public int size() {
return elements.length;
}
@Override public boolean isEmpty() {
return false;
}
/*
* The cast is safe because the only way to create an instance is via the
* create() method above, which only permits elements of type E.
*/
@SuppressWarnings("unchecked")
@Override public UnmodifiableIterator iterator() {
return (UnmodifiableIterator) Iterators.forArray(elements);
}
@Override public Object[] toArray() {
Object[] array = new Object[size()];
System.arraycopy(elements, 0, array, 0, size());
return array;
}
@Override public T[] toArray(T[] array) {
int size = size();
if (array.length < size) {
array = ObjectArrays.newArray(array, size);
} else if (array.length > size) {
array[size] = null;
}
System.arraycopy(elements, 0, array, 0, size);
return array;
}
@Override public boolean containsAll(Collection targets) {
if (targets == this) {
return true;
}
if (!(targets instanceof ArrayImmutableSet)) {
return super.containsAll(targets);
}
if (targets.size() > size()) {
return false;
}
for (Object target : ((ArrayImmutableSet) targets).elements) {
if (!contains(target)) {
return false;
}
}
return true;
}
@Override ImmutableList createAsList() {
return new ImmutableAsList(elements, this);
}
}
/** such as ImmutableMap.keySet() */
abstract static class TransformedImmutableSet extends ImmutableSet {
final D[] source;
final int hashCode;
TransformedImmutableSet(D[] source, int hashCode) {
this.source = source;
this.hashCode = hashCode;
}
abstract E transform(D element);
public int size() {
return source.length;
}
@Override public boolean isEmpty() {
return false;
}
@Override public UnmodifiableIterator iterator() {
return new AbstractIterator() {
int index = 0;
@Override protected E computeNext() {
return index < source.length
? transform(source[index++])
: endOfData();
}
};
}
@Override public Object[] toArray() {
return toArray(new Object[size()]);
}
@Override public T[] toArray(T[] array) {
int size = size();
if (array.length < size) {
array = ObjectArrays.newArray(array, size);
} else if (array.length > size) {
array[size] = null;
}
// Writes will produce ArrayStoreException when the toArray() doc requires
Object[] objectArray = array;
for (int i = 0; i < source.length; i++) {
objectArray[i] = transform(source[i]);
}
return array;
}
@Override public final int hashCode() {
return hashCode;
}
@Override boolean isHashCodeFast() {
return true;
}
}
/*
* 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.
*/
public static class Builder extends ImmutableCollection.Builder {
// accessed directly by ImmutableSortedSet
final ArrayList contents = Lists.newArrayList();
/**
* Creates a new builder. The returned builder is equivalent to the builder
* generated by {@link ImmutableSet#builder}.
*/
public Builder() {}
/**
* 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) {
contents.add(checkNotNull(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) {
contents.ensureCapacity(contents.size() + elements.length);
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) {
if (elements instanceof Collection) {
Collection collection = (Collection) elements;
contents.ensureCapacity(contents.size() + collection.size());
}
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() {
return copyOf(contents);
}
}
}