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Guava Collections is a collections extension library with expanded collection types, implementations, and utility methods for dealing with aggregate data.

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/*
 * 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.common.collect;

import com.google.common.annotations.GwtCompatible;

import java.util.Collection;
import java.util.Comparator;
import java.util.NoSuchElementException;
import java.util.Set;

import javax.annotation.Nullable;

/**
 * An empty immutable sorted set.
 *
 * @author Jared Levy
 */
@GwtCompatible(serializable = true, emulated = true)
@SuppressWarnings("serial") // uses writeReplace(), not default serialization
class EmptyImmutableSortedSet extends ImmutableSortedSet {
  EmptyImmutableSortedSet(Comparator comparator) {
    super(comparator);
  }

  public int size() {
    return 0;
  }

  @Override public boolean isEmpty() {
    return true;
  }

  @Override public boolean contains(Object target) {
    return false;
  }

  @Override public UnmodifiableIterator iterator() {
    return Iterators.emptyIterator();
  }

  private static final Object[] EMPTY_ARRAY = new Object[0];

  @Override public Object[] toArray() {
    return EMPTY_ARRAY;
  }

  @Override public  T[] toArray(T[] a) {
    if (a.length > 0) {
      a[0] = null;
    }
    return a;
  }

  @Override public boolean containsAll(Collection targets) {
    return targets.isEmpty();
  }

  @Override public boolean equals(@Nullable Object object) {
    if (object instanceof Set) {
      Set that = (Set) object;
      return that.isEmpty();
    }
    return false;
  }

  @Override public int hashCode() {
    return 0;
  }

  @Override public String toString() {
    return "[]";
  }

  public E first() {
    throw new NoSuchElementException();
  }

  public E last() {
    throw new NoSuchElementException();
  }

  @Override ImmutableSortedSet headSetImpl(E toElement) {
    return this;
  }

  @Override ImmutableSortedSet subSetImpl(E fromElement, E toElement) {
    return this;
  }

  @Override ImmutableSortedSet tailSetImpl(E fromElement) {
    return this;
  }

  @Override boolean hasPartialArray() {
    return false;
  }

  @Override int indexOf(Object target) {
    return -1;
  }
}