/*
* 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.inject.internal.util;
import java.io.Serializable;
import java.util.Collection;
import java.util.Iterator;
import java.util.NoSuchElementException;
/**
* An immutable collection. Does not permit null 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
*/
@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();
/** Copied here for GWT compatibility. */
private static final Object[] EMPTY_ARRAY = new Object[0];
private static final UnmodifiableIterator<Object> EMPTY_ITERATOR
= new UnmodifiableIterator<Object>() {
public boolean hasNext() {
return false;
}
public Object next() {
throw new NoSuchElementException();
}
};
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;
}
int index = 0;
for (E element : this) {
/*
* Sleazy fake cast. However, if element is not a T, then the very next
* line must fail with an ArrayStoreException, so we should be safe.
*/
@SuppressWarnings("unchecked")
T elementAsT = (T) element;
other[index++] = elementAsT;
}
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);
sb.append('[');
Iterator<E> i = iterator();
if (i.hasNext()) {
sb.append(i.next());
}
while (i.hasNext()) {
sb.append(", ");
sb.append(i.next());
}
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();
}
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 EMPTY_ITERATOR;
}
@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 new UnmodifiableIterator<E>() {
int i = 0;
public boolean hasNext() {
return i < elements.length;
}
public E next() {
if (!hasNext()) {
throw new NoSuchElementException();
}
return elements[i++];
}
};
}
}
/*
* 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>(elements.clone());
}
private static final long serialVersionUID = 0;
}
Object writeReplace() {
return new SerializedForm(toArray());
}
}