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      1 /*
      2  * Copyright (C) 2012 The Guava Authors
      3  *
      4  * Licensed under the Apache License, Version 2.0 (the "License");
      5  * you may not use this file except in compliance with the License.
      6  * You may obtain a copy of the License at
      7  *
      8  * http://www.apache.org/licenses/LICENSE-2.0
      9  *
     10  * Unless required by applicable law or agreed to in writing, software
     11  * distributed under the License is distributed on an "AS IS" BASIS,
     12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     13  * See the License for the specific language governing permissions and
     14  * limitations under the License.
     15  */
     16 package com.google.common.collect;
     17 
     18 import static com.google.common.base.Preconditions.checkNotNull;
     19 
     20 import com.google.common.annotations.GwtCompatible;
     21 
     22 import java.util.Comparator;
     23 
     24 import javax.annotation.Nullable;
     25 
     26 /**
     27  * An empty immutable sorted map.
     28  *
     29  * @author Louis Wasserman
     30  */
     31 @GwtCompatible(emulated = true)
     32 @SuppressWarnings("serial") // uses writeReplace, not default serialization
     33 final class EmptyImmutableSortedMap<K, V> extends ImmutableSortedMap<K, V> {
     34   private final transient ImmutableSortedSet<K> keySet;
     35 
     36   EmptyImmutableSortedMap(Comparator<? super K> comparator) {
     37     this.keySet = ImmutableSortedSet.emptySet(comparator);
     38   }
     39 
     40   EmptyImmutableSortedMap(
     41       Comparator<? super K> comparator, ImmutableSortedMap<K, V> descendingMap) {
     42     super(descendingMap);
     43     this.keySet = ImmutableSortedSet.emptySet(comparator);
     44   }
     45 
     46   @Override
     47   public V get(@Nullable Object key) {
     48     return null;
     49   }
     50 
     51   @Override
     52   public ImmutableSortedSet<K> keySet() {
     53     return keySet;
     54   }
     55 
     56   @Override
     57   public int size() {
     58     return 0;
     59   }
     60 
     61   @Override
     62   public boolean isEmpty() {
     63     return true;
     64   }
     65 
     66   @Override
     67   public ImmutableCollection<V> values() {
     68     return ImmutableList.of();
     69   }
     70 
     71   @Override
     72   public String toString() {
     73     return "{}";
     74   }
     75 
     76   @Override
     77   boolean isPartialView() {
     78     return false;
     79   }
     80 
     81   @Override
     82   public ImmutableSet<Entry<K, V>> entrySet() {
     83     return ImmutableSet.of();
     84   }
     85 
     86   @Override
     87   ImmutableSet<Entry<K, V>> createEntrySet() {
     88     throw new AssertionError("should never be called");
     89   }
     90 
     91   @Override
     92   public ImmutableSetMultimap<K, V> asMultimap() {
     93     return ImmutableSetMultimap.of();
     94   }
     95 
     96   @Override
     97   public ImmutableSortedMap<K, V> headMap(K toKey, boolean inclusive) {
     98     checkNotNull(toKey);
     99     return this;
    100   }
    101 
    102   @Override
    103   public ImmutableSortedMap<K, V> tailMap(K fromKey, boolean inclusive) {
    104     checkNotNull(fromKey);
    105     return this;
    106   }
    107 
    108   @Override
    109   ImmutableSortedMap<K, V> createDescendingMap() {
    110     return new EmptyImmutableSortedMap<K, V>(Ordering.from(comparator()).reverse(), this);
    111   }
    112 }
    113