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/*
 * Copyright (C) 2009 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 static com.google.common.base.Preconditions.checkNotNull;
import static com.google.common.collect.Iterators.singletonIterator;
import static java.util.Collections.singleton;

import com.google.common.annotations.GwtCompatible;
import com.google.common.annotations.GwtIncompatible;
import com.google.common.annotations.J2ktIncompatible;
import com.google.common.base.Preconditions;
import java.util.Spliterator;

/**
 * Implementation of {@link ImmutableList} with exactly one element.
 *
 * @author Hayward Chan
 */
@GwtCompatible(serializable = true, emulated = true)
@SuppressWarnings("serial") // uses writeReplace(), not default serialization
@ElementTypesAreNonnullByDefault
final class SingletonImmutableList extends ImmutableList {

  final transient E element;

  SingletonImmutableList(E element) {
    this.element = checkNotNull(element);
  }

  @Override
  public E get(int index) {
    Preconditions.checkElementIndex(index, 1);
    return element;
  }

  @Override
  public UnmodifiableIterator iterator() {
    return singletonIterator(element);
  }

  @Override
  public Spliterator spliterator() {
    return singleton(element).spliterator();
  }

  @Override
  public int size() {
    return 1;
  }

  @Override
  public ImmutableList subList(int fromIndex, int toIndex) {
    Preconditions.checkPositionIndexes(fromIndex, toIndex, 1);
    return (fromIndex == toIndex) ? ImmutableList.of() : this;
  }

  @Override
  public String toString() {
    return '[' + element.toString() + ']';
  }

  @Override
  boolean isPartialView() {
    return false;
  }

  // redeclare to help optimizers with b/310253115
  @SuppressWarnings("RedundantOverride")
  @Override
  @J2ktIncompatible // serialization
  @GwtIncompatible // serialization
  Object writeReplace() {
    return super.writeReplace();
  }
}