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/*
* Copyright (C) 2007 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 com.google.common.annotations.GwtCompatible;
import com.google.common.base.Preconditions;
import java.util.Set;
import javax.annotation.Nullable;
/**
* Implementation of {@link ImmutableSet} with exactly one element.
*
* @author Kevin Bourrillion
* @author Nick Kralevich
*/
@GwtCompatible(serializable = true, emulated = true)
@SuppressWarnings("serial") // uses writeReplace(), not default serialization
final class SingletonImmutableSet<E> extends ImmutableSet<E> {
final transient E element;
// This is transient because it will be recalculated on the first
// call to hashCode().
//
// A race condition is avoided since threads will either see that the value
// is zero and recalculate it themselves, or two threads will see it at
// the same time, and both recalculate it. If the cachedHashCode is 0,
// it will always be recalculated, unfortunately.
private transient int cachedHashCode;
SingletonImmutableSet(E element) {
this.element = Preconditions.checkNotNull(element);
}
SingletonImmutableSet(E element, int hashCode) {
// Guaranteed to be non-null by the presence of the pre-computed hash code.
this.element = element;
cachedHashCode = hashCode;
}
@Override
public int size() {
return 1;
}
@Override public boolean isEmpty() {
return false;
}
@Override public boolean contains(Object target) {
return element.equals(target);
}
@Override public UnmodifiableIterator<E> iterator() {
return Iterators.singletonIterator(element);
}
@Override boolean isPartialView() {
return false;
}
@Override public Object[] toArray() {
return new Object[] { element };
}
@Override public <T> T[] toArray(T[] array) {
if (array.length == 0) {
array = ObjectArrays.newArray(array, 1);
} else if (array.length > 1) {
array[1] = null;
}
// Writes will produce ArrayStoreException when the toArray() doc requires.
Object[] objectArray = array;
objectArray[0] = element;
return array;
}
@Override public boolean equals(@Nullable Object object) {
if (object == this) {
return true;
}
if (object instanceof Set) {
Set<?> that = (Set<?>) object;
return that.size() == 1 && element.equals(that.iterator().next());
}
return false;
}
@Override public final int hashCode() {
// Racy single-check.
int code = cachedHashCode;
if (code == 0) {
cachedHashCode = code = element.hashCode();
}
return code;
}
@Override boolean isHashCodeFast() {
return cachedHashCode != 0;
}
@Override public String toString() {
String elementToString = element.toString();
return new StringBuilder(elementToString.length() + 2)
.append('[')
.append(elementToString)
.append(']')
.toString();
}
}
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