/*
    * 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 java.util.Collection;
  import java.util.Set;
  
  import javax.annotation.Nullable;
  
  /**
   * An empty immutable set.
   *
   * @author Kevin Bourrillion
   */
  @GwtCompatible(serializable = true, emulated = true)
  final class EmptyImmutableSet extends ImmutableSet<Object> {
    static final EmptyImmutableSet INSTANCE = new EmptyImmutableSet();
  
    private EmptyImmutableSet() {}
  
    @Override
    public int size() {
      return 0;
    }
  
    @Override public boolean isEmpty() {
      return true;
    }
  
    @Override public boolean contains(@Nullable Object target) {
      return false;
    }
  
    @Override public boolean containsAll(Collection<?> targets) {
      return targets.isEmpty();
    }
  
    @Override public UnmodifiableIterator<Object> iterator() {
      return Iterators.emptyIterator();
    }
  
    @Override boolean isPartialView() {
      return false;
    }
  
    @Override
    int copyIntoArray(Object[] dst, int offset) {
      return offset;
    }
  
    @Override
    public ImmutableList<Object> asList() {
      return ImmutableList.of();
    }
  
    @Override public boolean equals(@Nullable Object object) {
      if (object instanceof Set) {
        Set<?> that = (Set<?>) object;
        return that.isEmpty();
      }
      return false;
    }
  
    @Override public final int hashCode() {
      return 0;
    }
  
    @Override boolean isHashCodeFast() {
      return true;
    }
  
    @Override public String toString() {
      return "[]";
    }
  
    Object readResolve() {
      return INSTANCE; // preserve singleton property
    }
  
    private static final long serialVersionUID = 0;
  }