/*
    * Copyright (C) 2008 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 javax.annotation.Nullable;
  
  /**
   * Bimap with no mappings.
   *
   * @author Jared Levy
   */
  @GwtCompatible(emulated = true)
  @SuppressWarnings("serial") // uses writeReplace(), not default serialization
  final class EmptyImmutableBiMap extends ImmutableBiMap<Object, Object> {
    static final EmptyImmutableBiMap INSTANCE = new EmptyImmutableBiMap();
  
    private EmptyImmutableBiMap() {}
    
    @Override public ImmutableBiMap<Object, Object> inverse() {
      return this;
    }
    
    @Override
    public int size() {
      return 0;
    }
  
    @Override
    public boolean isEmpty() {
      return true;
    }
  
    @Override
    public Object get(@Nullable Object key) {
      return null;
    }
  
    @Override
    public ImmutableSet<Entry<Object, Object>> entrySet() {
      return ImmutableSet.of();
    }
  
    @Override
    ImmutableSet<Entry<Object, Object>> createEntrySet() {
      throw new AssertionError("should never be called");
    }
  
    @Override
    public ImmutableSetMultimap<Object, Object> asMultimap() {
      return ImmutableSetMultimap.of();
    }
  
    @Override
    public ImmutableSet<Object> keySet() {
      return ImmutableSet.of();
    }
  
    @Override
    boolean isPartialView() {
      return false;
    }
    
    Object readResolve() {
      return INSTANCE; // preserve singleton property
    }
  }