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      1 /*
      2  * Copyright (C) 2008 Google Inc.
      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 
     17 package com.google.common.collect;
     18 
     19 import com.google.common.annotations.GwtCompatible;
     20 
     21 import java.util.Map;
     22 
     23 import javax.annotation.Nullable;
     24 
     25 import static com.google.common.base.Preconditions.checkNotNull;
     26 
     27 /**
     28  * Implementation of {@link ImmutableMap} with exactly one entry.
     29  *
     30  * @author Jesse Wilson
     31  * @author Kevin Bourrillion
     32  */
     33 @GwtCompatible(serializable = true)
     34 @SuppressWarnings("serial") // uses writeReplace(), not default serialization
     35 final class SingletonImmutableMap<K, V> extends ImmutableMap<K, V> {
     36   final transient K singleKey;
     37   final transient V singleValue;
     38 
     39   private transient Entry<K, V> entry;
     40 
     41   SingletonImmutableMap(K singleKey, V singleValue) {
     42     this.singleKey = singleKey;
     43     this.singleValue = singleValue;
     44   }
     45 
     46   SingletonImmutableMap(Entry<K, V> entry) {
     47     this.entry = checkNotNull(entry);  // checkNotNull for GWT.
     48     this.singleKey = checkNotNull(entry.getKey());  // checkNotNull for GWT.
     49     this.singleValue = checkNotNull(entry.getValue()); // checkNotNull for GWT.
     50   }
     51 
     52   private Entry<K, V> entry() {
     53     Entry<K, V> e = entry;
     54     return (e == null)
     55         ? (entry = Maps.immutableEntry(singleKey, singleValue)) : e;
     56   }
     57 
     58   @Override public V get(Object key) {
     59     return singleKey.equals(key) ? singleValue : null;
     60   }
     61 
     62   public int size() {
     63     return 1;
     64   }
     65 
     66   @Override public boolean isEmpty() {
     67     return false;
     68   }
     69 
     70   @Override public boolean containsKey(Object key) {
     71     return singleKey.equals(key);
     72   }
     73 
     74   @Override public boolean containsValue(Object value) {
     75     return singleValue.equals(value);
     76   }
     77 
     78   private transient ImmutableSet<Entry<K, V>> entrySet;
     79 
     80   @Override public ImmutableSet<Entry<K, V>> entrySet() {
     81     ImmutableSet<Entry<K, V>> es = entrySet;
     82     return (es == null) ? (entrySet = ImmutableSet.of(entry())) : es;
     83   }
     84 
     85   private transient ImmutableSet<K> keySet;
     86 
     87   @Override public ImmutableSet<K> keySet() {
     88     ImmutableSet<K> ks = keySet;
     89     return (ks == null) ? (keySet = ImmutableSet.of(singleKey)) : ks;
     90   }
     91 
     92   private transient ImmutableCollection<V> values;
     93 
     94   @Override public ImmutableCollection<V> values() {
     95     ImmutableCollection<V> v = values;
     96     return (v == null) ? (values = new Values<V>(singleValue)) : v;
     97   }
     98 
     99   @SuppressWarnings("serial") // uses writeReplace(), not default serialization
    100   private static class Values<V> extends ImmutableCollection<V> {
    101     final V singleValue;
    102 
    103     Values(V singleValue) {
    104       this.singleValue = singleValue;
    105     }
    106 
    107     @Override public boolean contains(Object object) {
    108       return singleValue.equals(object);
    109     }
    110 
    111     @Override public boolean isEmpty() {
    112       return false;
    113     }
    114 
    115     public int size() {
    116       return 1;
    117     }
    118 
    119     @Override public UnmodifiableIterator<V> iterator() {
    120       return Iterators.singletonIterator(singleValue);
    121     }
    122   }
    123 
    124   @Override public boolean equals(@Nullable Object object) {
    125     if (object == this) {
    126       return true;
    127     }
    128     if (object instanceof Map) {
    129       Map<?, ?> that = (Map<?, ?>) object;
    130       if (that.size() != 1) {
    131         return false;
    132       }
    133       Entry<?, ?> entry = that.entrySet().iterator().next();
    134       return singleKey.equals(entry.getKey())
    135           && singleValue.equals(entry.getValue());
    136     }
    137     return false;
    138   }
    139 
    140   @Override public int hashCode() {
    141     return singleKey.hashCode() ^ singleValue.hashCode();
    142   }
    143 
    144   @Override public String toString() {
    145     return new StringBuilder()
    146         .append('{')
    147         .append(singleKey.toString())
    148         .append('=')
    149         .append(singleValue.toString())
    150         .append('}')
    151         .toString();
    152   }
    153 }
    154