/*
* Copyright (C) 2008 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 com.google.common.annotations.GwtCompatible;
import static com.google.common.base.Preconditions.checkNotNull;
import java.io.Serializable;
import java.util.Collection;
import java.util.Iterator;
import javax.annotation.Nullable;
/**
* An immutable collection. Does not permit null elements.
*
* <p>In addition to the {@link Collection} methods, this class has an {@link
* #asList()} method, which returns a list view of the collection's elements.
*
* <p><b>Note</b>: Although this class is not final, it cannot be subclassed
* outside of this package as it has no public or protected constructors. Thus,
* instances of this type are guaranteed to be immutable.
*
* @author Jesse Wilson
* @since 2010.01.04 <b>stable</b> (imported from Google Collections Library)
*/
@GwtCompatible
@SuppressWarnings("serial") // we're overriding default serialization
public abstract class ImmutableCollection<E>
implements Collection<E>, Serializable {
static final ImmutableCollection<Object> EMPTY_IMMUTABLE_COLLECTION
= new EmptyImmutableCollection();
ImmutableCollection() {}
/**
* Returns an unmodifiable iterator across the elements in this collection.
*/
public abstract UnmodifiableIterator<E> iterator();
public Object[] toArray() {
Object[] newArray = new Object[size()];
return toArray(newArray);
}
public <T> T[] toArray(T[] other) {
int size = size();
if (other.length < size) {
other = ObjectArrays.newArray(other, size);
} else if (other.length > size) {
other[size] = null;
}
// Writes will produce ArrayStoreException when the toArray() doc requires.
Object[] otherAsObjectArray = other;
int index = 0;
for (E element : this) {
otherAsObjectArray[index++] = element;
}
return other;
}
public boolean contains(@Nullable Object object) {
if (object == null) {
return false;
}
for (E element : this) {
if (element.equals(object)) {
return true;
}
}
return false;
}
public boolean containsAll(Collection<?> targets) {
for (Object target : targets) {
if (!contains(target)) {
return false;
}
}
return true;
}
public boolean isEmpty() {
return size() == 0;
}
@Override public String toString() {
StringBuilder sb = new StringBuilder(size() * 16).append('[');
Collections2.standardJoiner.appendTo(sb, this);
return sb.append(']').toString();
}
/**
* Guaranteed to throw an exception and leave the collection unmodified.
*
* @throws UnsupportedOperationException always
*/
public final boolean add(E e) {
throw new UnsupportedOperationException();
}
/**
* Guaranteed to throw an exception and leave the collection unmodified.
*
* @throws UnsupportedOperationException always
*/
public final boolean remove(Object object) {
throw new UnsupportedOperationException();
}
/**
* Guaranteed to throw an exception and leave the collection unmodified.
*
* @throws UnsupportedOperationException always
*/
public final boolean addAll(Collection<? extends E> newElements) {
throw new UnsupportedOperationException();
}
/**
* Guaranteed to throw an exception and leave the collection unmodified.
*
* @throws UnsupportedOperationException always
*/
public final boolean removeAll(Collection<?> oldElements) {
throw new UnsupportedOperationException();
}
/**
* Guaranteed to throw an exception and leave the collection unmodified.
*
* @throws UnsupportedOperationException always
*/
public final boolean retainAll(Collection<?> elementsToKeep) {
throw new UnsupportedOperationException();
}
/**
* Guaranteed to throw an exception and leave the collection unmodified.
*
* @throws UnsupportedOperationException always
*/
public final void clear() {
throw new UnsupportedOperationException();
}
// TODO: Restructure code so ImmutableList doesn't contain this variable,
// which it doesn't use.
private transient ImmutableList<E> asList;
/**
* Returns a list view of the collection.
*
* @since 2010.01.04 <b>tentative</b>
*/
public ImmutableList<E> asList() {
ImmutableList<E> list = asList;
return (list == null) ? (asList = createAsList()) : list;
}
ImmutableList<E> createAsList() {
switch (size()) {
case 0:
return ImmutableList.of();
case 1:
return ImmutableList.of(iterator().next());
default:
return new ImmutableAsList<E>(toArray(), this);
}
}
private static class EmptyImmutableCollection
extends ImmutableCollection<Object> {
public int size() {
return 0;
}
@Override public boolean isEmpty() {
return true;
}
@Override public boolean contains(@Nullable Object object) {
return false;
}
@Override public UnmodifiableIterator<Object> iterator() {
return Iterators.EMPTY_ITERATOR;
}
private static final Object[] EMPTY_ARRAY = new Object[0];
@Override public Object[] toArray() {
return EMPTY_ARRAY;
}
@Override public <T> T[] toArray(T[] array) {
if (array.length > 0) {
array[0] = null;
}
return array;
}
}
private static class ArrayImmutableCollection<E>
extends ImmutableCollection<E> {
private final E[] elements;
ArrayImmutableCollection(E[] elements) {
this.elements = elements;
}
public int size() {
return elements.length;
}
@Override public boolean isEmpty() {
return false;
}
@Override public UnmodifiableIterator<E> iterator() {
return Iterators.forArray(elements);
}
}
/*
* Serializes ImmutableCollections as their logical contents. This ensures
* that implementation types do not leak into the serialized representation.
*/
private static class SerializedForm implements Serializable {
final Object[] elements;
SerializedForm(Object[] elements) {
this.elements = elements;
}
Object readResolve() {
return elements.length == 0
? EMPTY_IMMUTABLE_COLLECTION
: new ArrayImmutableCollection<Object>(Platform.clone(elements));
}
private static final long serialVersionUID = 0;
}
Object writeReplace() {
return new SerializedForm(toArray());
}
/**
* Abstract base class for builders of {@link ImmutableCollection} types.
*/
abstract static class Builder<E> {
/**
* 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
*/
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
*/
public Builder<E> add(E... elements) {
checkNotNull(elements); // for GWT
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
*/
public Builder<E> addAll(Iterable<? extends E> elements) {
checkNotNull(elements); // for GWT
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
*/
public Builder<E> addAll(Iterator<? extends E> elements) {
checkNotNull(elements); // for GWT
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();
}
}