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The Adobe Experience Manager SDK
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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
 *
 * @deprecated The Google Guava Core Libraries are deprecated and will not be part of the AEM SDK after April 2023
 */
@GwtCompatible(serializable = true, emulated = true)
// uses writeReplace(), not default serialization
@SuppressWarnings("serial")
@Deprecated(since = "2022-12-01")
final class SingletonImmutableSet extends ImmutableSet {

    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 iterator() {
        return Iterators.singletonIterator(element);
    }

    @Override
    boolean isPartialView() {
        return false;
    }

    @Override
    int copyIntoArray(Object[] dst, int offset) {
        dst[offset] = element;
        return offset + 1;
    }

    @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();
    }
}