/*
* Copyright (C) 2008 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.checkNotNull;
import static com.google.common.collect.CollectPreconditions.checkNonnegative;
import static com.google.common.collect.ObjectArrays.checkElementsNotNull;
import com.google.common.annotations.GwtCompatible;
import com.google.errorprone.annotations.CanIgnoreReturnValue;
import java.io.Serializable;
import java.util.AbstractCollection;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
import java.util.Collections;
import java.util.Iterator;
import java.util.List;
import java.util.Spliterator;
import java.util.Spliterators;
import java.util.function.Predicate;
import javax.annotation.Nullable;
/**
* A {@link Collection} whose contents will never change, and which offers a few additional
* guarantees detailed below.
*
* <p><b>Warning:</b> avoid <i>direct</i> usage of {@link ImmutableCollection} as a type (just as
* with {@link Collection} itself). Prefer subtypes such as {@link ImmutableSet} or {@link
* ImmutableList}, which have well-defined {@link #equals} semantics, thus avoiding a common source
* of bugs and confusion.
*
* <h3>About <i>all</i> {@code Immutable-} collections</h3>
*
* <p>The remainder of this documentation applies to every public {@code Immutable-} type in this
* package, whether it is a subtype of {@code ImmutableCollection} or not.
*
* <h4>Guarantees</h4>
*
* <p>Each makes the following guarantees:
*
* <ul>
* <li><b>Shallow immutability.</b> Elements can never be added, removed or replaced in this
* collection. This is a stronger guarantee than that of
* {@link Collections#unmodifiableCollection}, whose contents change whenever the wrapped
* collection is modified.
* <li><b>Null-hostility.</b> This collection will never contain a null element.
* <li><b>Deterministic iteration.</b> The iteration order is always well-defined, depending on how
* the collection was created (see the appropriate factory method for details). View collections
* such as {@link ImmutableMultiset#elementSet} iterate in the same order as the parent, except
* as noted.
* <li><b>Thread safety.</b> It is safe to access this collection concurrently from multiple
* threads.
* <li><b>Integrity.</b> This type cannot be subclassed outside this package (which would allow
* these guarantees to be violated).
* </ul>
*
* <h4>"Interfaces", not implementations</h4>
*
* <p>Each public class, such as {@link ImmutableSet}, is a <i>type</i> offering meaningful
* behavioral guarantees -- not merely a specific <i>implementation</i> as in the case of, say,
* {@link ArrayList}. You should treat them as interfaces in every important sense of the word.
*
* <p>For field types and method return types, you should generally use the immutable type (such as
* {@link ImmutableList}) instead of the general collection interface type (such as {@link List}).
* This communicates to your callers all of the semantic guarantees listed above, which is almost
* always very useful information.
*
* <p>On the other hand, a <i>parameter</i> type of {@link ImmutableList} is generally a nuisance to
* callers. Instead, accept {@link Iterable} and have your method or constructor body pass it to the
* appropriate {@code copyOf} method itself.
*
* <h4>Creation</h4>
*
* <p>Except for logically "abstract" types like {@code ImmutableCollection} itself, each {@code
* Immutable} type provides the static operations you need to obtain instances of that type. These
* usually include:
*
* <ul>
* <li>Static methods named {@code of}, accepting an explicit list of elements or entries.
* <li>Static methods named {@code copyOf} (or {@code copyOfSorted}), accepting an existing
* collection whose contents should be copied.
* <li>A static nested {@code Builder} class which can be used to populate a new immutable instance.
* </ul>
*
* <h4>Warnings</h4>
*
* <ul>
* <li><b>Warning:</b> as with any collection, it is almost always a bad idea to modify an element
* (in a way that affects its {@link Object#equals} behavior) while it is contained in a
* collection. Undefined behavior and bugs will result. It's generally best to avoid using
* mutable objects as elements at all, as many users may expect your "immutable" object to be
* <i>deeply</i> immutable.
* </ul>
*
* <h4>Performance notes</h4>
*
* <ul>
* <li>Implementations can be generally assumed to prioritize memory efficiency, then speed of
* access, and lastly speed of creation.
* <li>The {@code copyOf} methods 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.
* <li><b>Warning:</b> a view collection such as {@link ImmutableMap#keySet} or {@link
* ImmutableList#subList} may retain a reference to the entire data set, preventing it from
* being garbage collected. If some of the data is no longer reachable through other means, this
* constitutes a memory leak. Pass the view collection to the appropriate {@code copyOf} method
* to obtain a correctly-sized copy.
* <li>The performance of using the associated {@code Builder} class can be assumed to be
* no worse, and possibly better, than creating a mutable collection and copying it.
* <li>Implementations generally do not cache hash codes. If your element or key type has a slow
* {@code hashCode} implementation, it should cache it itself.
* </ul>
*
* <h4>Example usage</h4>
*
* <pre> {@code
*
* class Foo {
* private static final ImmutableSet<String> RESERVED_CODES =
* ImmutableSet.of("AZ", "CQ", "ZX");
*
* private final ImmutableSet<String> codes;
*
* public Foo(Iterable<String> codes) {
* this.codes = ImmutableSet.copyOf(codes);
* checkArgument(Collections.disjoint(this.codes, RESERVED_CODES));
* }
* }}</pre>
*
* <h3>See also</h3>
*
* <p>See the Guava User Guide article on <a href=
* "https://github.com/google/guava/wiki/ImmutableCollectionsExplained">
* immutable collections</a>.
*
* @since 2.0
*/
@GwtCompatible(emulated = true)
@SuppressWarnings("serial") // we're overriding default serialization
// TODO(kevinb): I think we should push everything down to "BaseImmutableCollection" or something,
// just to do everything we can to emphasize the "practically an interface" nature of this class.
public abstract class ImmutableCollection<E> extends AbstractCollection<E> implements Serializable {
/*
* We expect SIZED (and SUBSIZED, if applicable) to be added by the spliterator factory methods.
* These are properties of the collection as a whole; SIZED and SUBSIZED are more properties of
* the spliterator implementation.
*/
static final int SPLITERATOR_CHARACTERISTICS =
Spliterator.IMMUTABLE | Spliterator.NONNULL | Spliterator.ORDERED;
ImmutableCollection() {}
/**
* Returns an unmodifiable iterator across the elements in this collection.
*/
@Override
public abstract UnmodifiableIterator<E> iterator();
@Override
public Spliterator<E> spliterator() {
return Spliterators.spliterator(this, SPLITERATOR_CHARACTERISTICS);
}
private static final Object[] EMPTY_ARRAY = {};
@Override
public final Object[] toArray() {
int size = size();
if (size == 0) {
return EMPTY_ARRAY;
}
Object[] result = new Object[size];
copyIntoArray(result, 0);
return result;
}
@CanIgnoreReturnValue
@Override
public final <T> T[] toArray(T[] other) {
checkNotNull(other);
int size = size();
if (other.length < size) {
other = ObjectArrays.newArray(other, size);
} else if (other.length > size) {
other[size] = null;
}
copyIntoArray(other, 0);
return other;
}
@Override
public abstract boolean contains(@Nullable Object object);
/**
* Guaranteed to throw an exception and leave the collection unmodified.
*
* @throws UnsupportedOperationException always
* @deprecated Unsupported operation.
*/
@CanIgnoreReturnValue
@Deprecated
@Override
public final boolean add(E e) {
throw new UnsupportedOperationException();
}
/**
* Guaranteed to throw an exception and leave the collection unmodified.
*
* @throws UnsupportedOperationException always
* @deprecated Unsupported operation.
*/
@CanIgnoreReturnValue
@Deprecated
@Override
public final boolean remove(Object object) {
throw new UnsupportedOperationException();
}
/**
* Guaranteed to throw an exception and leave the collection unmodified.
*
* @throws UnsupportedOperationException always
* @deprecated Unsupported operation.
*/
@CanIgnoreReturnValue
@Deprecated
@Override
public final boolean addAll(Collection<? extends E> newElements) {
throw new UnsupportedOperationException();
}
/**
* Guaranteed to throw an exception and leave the collection unmodified.
*
* @throws UnsupportedOperationException always
* @deprecated Unsupported operation.
*/
@CanIgnoreReturnValue
@Deprecated
@Override
public final boolean removeAll(Collection<?> oldElements) {
throw new UnsupportedOperationException();
}
/**
* Guaranteed to throw an exception and leave the collection unmodified.
*
* @throws UnsupportedOperationException always
* @deprecated Unsupported operation.
*/
@CanIgnoreReturnValue
@Deprecated
@Override
public final boolean removeIf(Predicate<? super E> filter) {
throw new UnsupportedOperationException();
}
/**
* Guaranteed to throw an exception and leave the collection unmodified.
*
* @throws UnsupportedOperationException always
* @deprecated Unsupported operation.
*/
@Deprecated
@Override
public final boolean retainAll(Collection<?> elementsToKeep) {
throw new UnsupportedOperationException();
}
/**
* Guaranteed to throw an exception and leave the collection unmodified.
*
* @throws UnsupportedOperationException always
* @deprecated Unsupported operation.
*/
@Deprecated
@Override
public final void clear() {
throw new UnsupportedOperationException();
}
/**
* Returns an {@code ImmutableList} containing the same elements, in the same order, as this
* collection.
*
* <p><b>Performance note:</b> in most cases this method can return quickly without actually
* copying anything. The exact circumstances under which the copy is performed are undefined and
* subject to change.
*
* @since 2.0
*/
public ImmutableList<E> asList() {
switch (size()) {
case 0:
return ImmutableList.of();
case 1:
return ImmutableList.of(iterator().next());
default:
return new RegularImmutableAsList<E>(this, toArray());
}
}
/**
* Returns {@code true} if this immutable collection's implementation contains references to
* user-created objects that aren't accessible via this collection's methods. This is generally
* used to determine whether {@code copyOf} implementations should make an explicit copy to avoid
* memory leaks.
*/
abstract boolean isPartialView();
/**
* Copies the contents of this immutable collection into the specified array at the specified
* offset. Returns {@code offset + size()}.
*/
@CanIgnoreReturnValue
int copyIntoArray(Object[] dst, int offset) {
for (E e : this) {
dst[offset++] = e;
}
return offset;
}
Object writeReplace() {
// We serialize by default to ImmutableList, the simplest thing that works.
return new ImmutableList.SerializedForm(toArray());
}
/**
* Abstract base class for builders of {@link ImmutableCollection} types.
*
* @since 10.0
*/
public abstract static class Builder<E> {
static final int DEFAULT_INITIAL_CAPACITY = 4;
static int expandedCapacity(int oldCapacity, int minCapacity) {
if (minCapacity < 0) {
throw new AssertionError("cannot store more than MAX_VALUE elements");
}
// careful of overflow!
int newCapacity = oldCapacity + (oldCapacity >> 1) + 1;
if (newCapacity < minCapacity) {
newCapacity = Integer.highestOneBit(minCapacity - 1) << 1;
}
if (newCapacity < 0) {
newCapacity = Integer.MAX_VALUE;
// guaranteed to be >= newCapacity
}
return newCapacity;
}
Builder() {}
/**
* Adds {@code element} to the {@code ImmutableCollection} being built.
*
* <p>Note that each builder class covariantly returns its own type from
* this method.
*
* @param element the element to add
* @return this {@code Builder} instance
* @throws NullPointerException if {@code element} is null
*/
@CanIgnoreReturnValue
public abstract Builder<E> add(E element);
/**
* Adds each element of {@code elements} to the {@code ImmutableCollection}
* being built.
*
* <p>Note that each builder class overrides this method in order to
* covariantly return its own type.
*
* @param elements the elements to add
* @return this {@code Builder} instance
* @throws NullPointerException if {@code elements} is null or contains a
* null element
*/
@CanIgnoreReturnValue
public Builder<E> add(E... elements) {
for (E element : elements) {
add(element);
}
return this;
}
/**
* Adds each element of {@code elements} to the {@code ImmutableCollection}
* being built.
*
* <p>Note that each builder class overrides this method in order to
* covariantly return its own type.
*
* @param elements the elements to add
* @return this {@code Builder} instance
* @throws NullPointerException if {@code elements} is null or contains a
* null element
*/
@CanIgnoreReturnValue
public Builder<E> addAll(Iterable<? extends E> elements) {
for (E element : elements) {
add(element);
}
return this;
}
/**
* Adds each element of {@code elements} to the {@code ImmutableCollection}
* being built.
*
* <p>Note that each builder class overrides this method in order to
* covariantly return its own type.
*
* @param elements the elements to add
* @return this {@code Builder} instance
* @throws NullPointerException if {@code elements} is null or contains a
* null element
*/
@CanIgnoreReturnValue
public Builder<E> addAll(Iterator<? extends E> elements) {
while (elements.hasNext()) {
add(elements.next());
}
return this;
}
/**
* Returns a newly-created {@code ImmutableCollection} of the appropriate
* type, containing the elements provided to this builder.
*
* <p>Note that each builder class covariantly returns the appropriate type
* of {@code ImmutableCollection} from this method.
*/
public abstract ImmutableCollection<E> build();
}
abstract static class ArrayBasedBuilder<E> extends ImmutableCollection.Builder<E> {
Object[] contents;
int size;
ArrayBasedBuilder(int initialCapacity) {
checkNonnegative(initialCapacity, "initialCapacity");
this.contents = new Object[initialCapacity];
this.size = 0;
}
/**
* Expand the absolute capacity of the builder so it can accept at least
* the specified number of elements without being resized.
*/
private void ensureCapacity(int minCapacity) {
if (contents.length < minCapacity) {
this.contents =
Arrays.copyOf(
this.contents, expandedCapacity(contents.length, minCapacity));
}
}
@CanIgnoreReturnValue
@Override
public ArrayBasedBuilder<E> add(E element) {
checkNotNull(element);
ensureCapacity(size + 1);
contents[size++] = element;
return this;
}
@CanIgnoreReturnValue
@Override
public Builder<E> add(E... elements) {
checkElementsNotNull(elements);
ensureCapacity(size + elements.length);
System.arraycopy(elements, 0, contents, size, elements.length);
size += elements.length;
return this;
}
@CanIgnoreReturnValue
@Override
public Builder<E> addAll(Iterable<? extends E> elements) {
if (elements instanceof Collection) {
Collection<?> collection = (Collection<?>) elements;
ensureCapacity(size + collection.size());
}
super.addAll(elements);
return this;
}
@CanIgnoreReturnValue
ArrayBasedBuilder<E> combine(ArrayBasedBuilder<E> builder) {
checkNotNull(builder);
ensureCapacity(size + builder.size);
System.arraycopy(builder.contents, 0, this.contents, size, builder.size);
size += builder.size;
return this;
}
}
}