121 lines
3.0 KiB
Java
121 lines
3.0 KiB
Java
/*
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* Copyright (C) 2007 The Guava Authors
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package com.google.common.collect;
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import java.util.Set;
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import javax.annotation.Nullable;
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import com.google.common.annotations.GwtCompatible;
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import com.google.common.base.Preconditions;
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/**
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* Implementation of {@link ImmutableSet} with exactly one element.
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*
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* @author Kevin Bourrillion
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* @author Nick Kralevich
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*/
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@GwtCompatible(serializable = true, emulated = true)
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@SuppressWarnings("serial") // uses writeReplace(), not default serialization
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final class SingletonImmutableSet<E> extends ImmutableSet<E> {
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final transient E element;
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// This is transient because it will be recalculated on the first
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// call to hashCode().
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//
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// A race condition is avoided since threads will either see that the value
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// is zero and recalculate it themselves, or two threads will see it at
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// the same time, and both recalculate it. If the cachedHashCode is 0,
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// it will always be recalculated, unfortunately.
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private transient int cachedHashCode;
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SingletonImmutableSet(E element) {
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this.element = Preconditions.checkNotNull(element);
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}
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SingletonImmutableSet(E element, int hashCode) {
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// Guaranteed to be non-null by the presence of the pre-computed hash code.
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this.element = element;
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cachedHashCode = hashCode;
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}
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@Override
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public int size() {
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return 1;
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}
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@Override
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public boolean isEmpty() {
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return false;
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}
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@Override
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public boolean contains(Object target) {
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return element.equals(target);
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}
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@Override
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public UnmodifiableIterator<E> iterator() {
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return Iterators.singletonIterator(element);
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}
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@Override
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boolean isPartialView() {
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return false;
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}
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@Override
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int copyIntoArray(Object[] dst, int offset) {
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dst[offset] = element;
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return offset + 1;
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}
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@Override
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public boolean equals(@Nullable Object object) {
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if (object == this) {
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return true;
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}
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if (object instanceof Set) {
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Set<?> that = (Set<?>) object;
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return that.size() == 1 && element.equals(that.iterator().next());
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}
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return false;
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}
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@Override
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public final int hashCode() {
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// Racy single-check.
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int code = cachedHashCode;
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if (code == 0) {
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cachedHashCode = code = element.hashCode();
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}
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return code;
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}
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@Override
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boolean isHashCodeFast() {
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return cachedHashCode != 0;
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}
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@Override
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public String toString() {
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String elementToString = element.toString();
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return new StringBuilder(elementToString.length() + 2).append('[').append(elementToString).append(']')
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.toString();
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}
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}
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