/*
 * 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 org.checkerframework.checker.nullness.qual.Nullable;

Implementation of Entry for ImmutableMap that adds extra methods to traverse hash buckets for the key and the value. This allows reuse in RegularImmutableMap and RegularImmutableBiMap, which don't have to recopy the entries created by their Builder implementations. 
This base implementation has no key or value pointers, so instances of ImmutableMapEntry (but
not its subclasses) can be reused when copied from one ImmutableMap to another.
Author:
Louis Wasserman/**
 * Implementation of {@code 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.
 *
 * <p>This base implementation has no key or value pointers, so instances of ImmutableMapEntry (but
 * not its subclasses) can be reused when copied from one ImmutableMap to another.
 *
 * @author Louis Wasserman
 */
@GwtIncompatible // unnecessary
class ImmutableMapEntry<K, V> extends ImmutableEntry<K, V> {
  
Creates an ImmutableMapEntry array to hold parameterized entries. The result must never be upcast back to ImmutableMapEntry[] (or Object[], etc.), or allowed to escape the class. /**
   * Creates an {@code ImmutableMapEntry} array to hold parameterized entries. The result must never
   * be upcast back to ImmutableMapEntry[] (or Object[], etc.), or allowed to escape the class.
   */
  @SuppressWarnings("unchecked") // Safe as long as the javadocs are followed
  static <K, V> ImmutableMapEntry<K, V>[] createEntryArray(int size) {
    return new ImmutableMapEntry[size];
  }

  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
  ImmutableMapEntry<K, V> getNextInKeyBucket() {
    return null;
  }

  @Nullable
  ImmutableMapEntry<K, V> getNextInValueBucket() {
    return null;
  }

  
Returns true if this entry has no bucket links and can safely be reused as a terminal entry in
a bucket in another map.
/**
   * Returns true if this entry has no bucket links and can safely be reused as a terminal entry in
   * a bucket in another map.
   */
  boolean isReusable() {
    return true;
  }

  static class NonTerminalImmutableMapEntry<K, V> extends ImmutableMapEntry<K, V> {
    private final transient ImmutableMapEntry<K, V> nextInKeyBucket;

    NonTerminalImmutableMapEntry(K key, V value, ImmutableMapEntry<K, V> nextInKeyBucket) {
      super(key, value);
      this.nextInKeyBucket = nextInKeyBucket;
    }

    @Override
    final @Nullable ImmutableMapEntry<K, V> getNextInKeyBucket() {
      return nextInKeyBucket;
    }

    @Override
    final boolean isReusable() {
      return false;
    }
  }

  static final class NonTerminalImmutableBiMapEntry<K, V>
      extends NonTerminalImmutableMapEntry<K, V> {
    private final transient ImmutableMapEntry<K, V> nextInValueBucket;

    NonTerminalImmutableBiMapEntry(
        K key,
        V value,
        ImmutableMapEntry<K, V> nextInKeyBucket,
        ImmutableMapEntry<K, V> nextInValueBucket) {
      super(key, value, nextInKeyBucket);
      this.nextInValueBucket = nextInValueBucket;
    }

    @Override
    @Nullable
    ImmutableMapEntry<K, V> getNextInValueBucket() {
      return nextInValueBucket;
    }
  }
}