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/*
* 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 com.google.common.annotations.GwtCompatible;
import com.google.errorprone.annotations.CanIgnoreReturnValue;
import com.google.errorprone.annotations.DoNotCall;
import com.google.errorprone.annotations.DoNotMock;
import java.io.Serializable;
import java.util.AbstractCollection;
import java.util.Collection;
import java.util.Collections;
import java.util.HashSet;
import java.util.Iterator;
import java.util.List;
import java.util.Spliterator;
import java.util.Spliterators;
import java.util.function.Predicate;
import javax.annotation.CheckForNull;
import org.checkerframework.checker.nullness.qual.Nullable;
/**
* A {@link Collection} whose contents will never change, and which offers a few additional
* guarantees detailed below.
*
* Warning: avoid direct 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.
*
*
About all {@code Immutable-} collections
*
* 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.
*
*
Guarantees
*
* Each makes the following guarantees:
*
*
* - Shallow immutability. 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.
*
- Null-hostility. This collection will never contain a null element.
*
- Deterministic iteration. The iteration order is always well-defined, depending on
* how the collection was created. Typically this is insertion order unless an explicit
* ordering is otherwise specified (e.g. {@link ImmutableSortedSet#naturalOrder}). 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.
*
- Thread safety. It is safe to access this collection concurrently from multiple
* threads.
*
- Integrity. This type cannot be subclassed outside this package (which would allow
* these guarantees to be violated).
*
*
* "Interfaces", not implementations
*
* These are classes instead of interfaces to prevent external subtyping, but should be thought
* of as interfaces in every important sense. Each public class such as {@link ImmutableSet} is a
* type offering meaningful behavioral guarantees. This is substantially different from the
* case of (say) {@link HashSet}, which is an implementation, with semantics that were
* largely defined by its supertype.
*
*
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.
*
*
On the other hand, a parameter 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.
*
*
Expressing the immutability guarantee directly in the type that user code references is a
* powerful advantage. Although Java offers certain immutable collection factory methods, such as
* {@link Collections#singleton(Object)} and {@code Set.of},
* we recommend using these classes instead for this reason (as well as for consistency).
*
*
Creation
*
* 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:
*
*
* - Static methods named {@code of}, accepting an explicit list of elements or entries.
*
- Static methods named {@code copyOf} (or {@code copyOfSorted}), accepting an existing
* collection whose contents should be copied.
*
- A static nested {@code Builder} class which can be used to populate a new immutable
* instance.
*
*
* Warnings
*
*
* - Warning: 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
* deeply immutable.
*
*
* Performance notes
*
*
* - Implementations can be generally assumed to prioritize memory efficiency, then speed of
* access, and lastly speed of creation.
*
- 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.
*
- Warning: 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.
*
- 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.
*
- Implementations generally do not cache hash codes. If your element or key type has a slow
* {@code hashCode} implementation, it should cache it itself.
*
*
* Example usage
*
* {@code
* class Foo {
* private static final ImmutableSet RESERVED_CODES =
* ImmutableSet.of("AZ", "CQ", "ZX");
*
* private final ImmutableSet codes;
*
* public Foo(Iterable codes) {
* this.codes = ImmutableSet.copyOf(codes);
* checkArgument(Collections.disjoint(this.codes, RESERVED_CODES));
* }
* }
* }
*
* See also
*
* See the Guava User Guide article on immutable collections.
*
* @since 2.0
*/
@DoNotMock("Use ImmutableList.of or another implementation")
@GwtCompatible(emulated = true)
@SuppressWarnings("serial") // we're overriding default serialization
@ElementTypesAreNonnullByDefault
// 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 extends AbstractCollection 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 iterator();
@Override
public Spliterator spliterator() {
return Spliterators.spliterator(this, SPLITERATOR_CHARACTERISTICS);
}
private static final Object[] EMPTY_ARRAY = {};
@Override
public final Object[] toArray() {
return toArray(EMPTY_ARRAY);
}
@CanIgnoreReturnValue
@Override
/*
* This suppression is here for two reasons:
*
* 1. b/192354773 in our checker affects toArray declarations.
*
* 2. `other[size] = null` is unsound. We could "fix" this by requiring callers to pass in an
* array with a nullable element type. But probably they usually want an array with a non-nullable
* type. That said, we could *accept* a `@Nullable T[]` (which, given that we treat arrays as
* covariant, would still permit a plain `T[]`) and return a plain `T[]`. But of course that would
* require its own suppression, since it is also unsound. toArray(T[]) is just a mess from a
* nullness perspective. The signature below at least has the virtue of being relatively simple.
*/
@SuppressWarnings("nullness")
public final T[] toArray(T[] other) {
checkNotNull(other);
int size = size();
if (other.length < size) {
Object[] internal = internalArray();
if (internal != null) {
return Platform.copy(internal, internalArrayStart(), internalArrayEnd(), other);
}
other = ObjectArrays.newArray(other, size);
} else if (other.length > size) {
other[size] = null;
}
copyIntoArray(other, 0);
return other;
}
/** If this collection is backed by an array of its elements in insertion order, returns it. */
@CheckForNull
Object[] internalArray() {
return null;
}
/**
* If this collection is backed by an array of its elements in insertion order, returns the offset
* where this collection's elements start.
*/
int internalArrayStart() {
throw new UnsupportedOperationException();
}
/**
* If this collection is backed by an array of its elements in insertion order, returns the offset
* where this collection's elements end.
*/
int internalArrayEnd() {
throw new UnsupportedOperationException();
}
@Override
public abstract boolean contains(@CheckForNull Object object);
/**
* Guaranteed to throw an exception and leave the collection unmodified.
*
* @throws UnsupportedOperationException always
* @deprecated Unsupported operation.
*/
@CanIgnoreReturnValue
@Deprecated
@Override
@DoNotCall("Always throws UnsupportedOperationException")
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
@DoNotCall("Always throws UnsupportedOperationException")
public final boolean remove(@CheckForNull Object object) {
throw new UnsupportedOperationException();
}
/**
* Guaranteed to throw an exception and leave the collection unmodified.
*
* @throws UnsupportedOperationException always
* @deprecated Unsupported operation.
*/
@CanIgnoreReturnValue
@Deprecated
@Override
@DoNotCall("Always throws UnsupportedOperationException")
public final boolean addAll(Collection newElements) {
throw new UnsupportedOperationException();
}
/**
* Guaranteed to throw an exception and leave the collection unmodified.
*
* @throws UnsupportedOperationException always
* @deprecated Unsupported operation.
*/
@CanIgnoreReturnValue
@Deprecated
@Override
@DoNotCall("Always throws UnsupportedOperationException")
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
@DoNotCall("Always throws UnsupportedOperationException")
public final boolean removeIf(Predicate filter) {
throw new UnsupportedOperationException();
}
/**
* Guaranteed to throw an exception and leave the collection unmodified.
*
* @throws UnsupportedOperationException always
* @deprecated Unsupported operation.
*/
@Deprecated
@Override
@DoNotCall("Always throws UnsupportedOperationException")
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
@DoNotCall("Always throws UnsupportedOperationException")
public final void clear() {
throw new UnsupportedOperationException();
}
/**
* Returns an {@code ImmutableList} containing the same elements, in the same order, as this
* collection.
*
* Performance note: 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 asList() {
switch (size()) {
case 0:
return ImmutableList.of();
case 1:
return ImmutableList.of(iterator().next());
default:
return new RegularImmutableAsList(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(@Nullable 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
*/
@DoNotMock
public abstract static class Builder {
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.
*
* 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 add(E element);
/**
* Adds each element of {@code elements} to the {@code ImmutableCollection} being built.
*
* 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 add(E... elements) {
for (E element : elements) {
add(element);
}
return this;
}
/**
* Adds each element of {@code elements} to the {@code ImmutableCollection} being built.
*
* 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 addAll(Iterable elements) {
for (E element : elements) {
add(element);
}
return this;
}
/**
* Adds each element of {@code elements} to the {@code ImmutableCollection} being built.
*
* 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 addAll(Iterator 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.
*
* Note that each builder class covariantly returns the appropriate type of {@code
* ImmutableCollection} from this method.
*/
public abstract ImmutableCollection build();
}
}