/*
    * Copyright (C) 2013 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.collect.CollectPreconditions.checkEntryNotNull;
  
  import com.google.common.annotations.GwtIncompatible;
  
  import javax.annotation.Nullable;
  
  /**
   * Implementation of {@code Map.Entry} for {@link ImmutableMap} that adds extra methods to traverse
   * hash buckets for the key and the value. This allows reuse in {@link RegularImmutableMap} and
   * {@link RegularImmutableBiMap}, which don't have to recopy the entries created by their
   * {@code Builder} implementations.
   *
   * @author Louis Wasserman
   */
  @GwtIncompatible("unnecessary")
  abstract class ImmutableMapEntry<K, V> extends ImmutableEntry<K, V> {
    ImmutableMapEntry(K key, V value) {
      super(key, value);
      checkEntryNotNull(key, value);
    }
  
    ImmutableMapEntry(ImmutableMapEntry<K, V> contents) {
      super(contents.getKey(), contents.getValue());
      // null check would be redundant
    }
  
    @Nullable
    abstract ImmutableMapEntry<K, V> getNextInKeyBucket();
  
    @Nullable
    abstract ImmutableMapEntry<K, V> getNextInValueBucket();
  
    static final class TerminalEntry<K, V> extends ImmutableMapEntry<K, V> {
      TerminalEntry(ImmutableMapEntry<K, V> contents) {
        super(contents);
      }
  
      TerminalEntry(K key, V value) {
        super(key, value);
      }
  
      @Override
      @Nullable
      ImmutableMapEntry<K, V> getNextInKeyBucket() {
        return null;
      }
  
      @Override
      @Nullable
      ImmutableMapEntry<K, V> getNextInValueBucket() {
        return null;
      }
    }
  }