简单hashmap实现

Posted 2020-12-09 bloch

学习于java编程思想

  1 import java.io.Serializable;
  2 import java.util.*;
  3 
  4 /**
  5  * 简单散列Map
  6  *
  7  * @param <K>
  8  * @param <V>
  9  */
 10 public class SimpleHashMap<K, V> extends AbstractMap<K, V> implements Serializable {
 11   private static final long serialVersionUID = -7250646258928392838L;
 12   static final int SIZE = 997;
 13 
 14   LinkedList<MapEntry<K, V>>[] buckets = new LinkedList[SIZE];
 15 
 16   @Override
 17   public V get(Object key) {
 18     int index = Math.abs(key.hashCode()) % SIZE;
 19     if (buckets[index] == null) {
 20       return null;
 21     }
 22     for (MapEntry<K, V> iPair : buckets[index]) {
 23       if (iPair.getKey().equals(key)) {
 24         return iPair.getValue();
 25       }
 26     }
 27     return null;
 28   }
 29 
 30   @Override
 31   public V put(K key, V value) {
 32     V oldValue = null;
 33     int index = Math.abs(key.hashCode()) % SIZE;
 34     if (buckets[index] == null) {
 35       buckets[index] = new LinkedList<>();
 36     }
 37     LinkedList<MapEntry<K, V>> bucket = buckets[index];
 38     MapEntry<K, V> pair = new MapEntry<>(key, value);
 39     boolean found = false;
 40     ListIterator<MapEntry<K, V>> it = bucket.listIterator();
 41     while (it.hasNext()) {
 42       MapEntry<K, V> iPair = it.next();
 43       if (iPair.getKey().equals(key)) {
 44         oldValue = iPair.getValue();
 45         it.set(pair);
 46         found = true;
 47         break;
 48       }
 49     }
 50     if (!found) {
 51       buckets[index].add(pair);
 52     }
 53 
 54     return oldValue;
 55   }
 56 
 57   @Override
 58   public Set<Entry<K, V>> entrySet() {
 59     Set<Entry<K, V>> set = new HashSet<>();
 60     for (LinkedList<MapEntry<K, V>> bucket : buckets) {
 61       if (bucket == null) {
 62         continue;
 63       }
 64       for (MapEntry<K, V> mpair : bucket) {
 65         set.add(mpair);
 66       }
 67     }
 68     return set;
 69   }
 70 
 71   public static void main(String[] args) {
 72     Map<String, String> map = new SimpleHashMap<>();
 73     map.put("a", "32");
 74     System.out.println(map.get("a"));
 75   }
 76 
 77   static class MapEntry<K, V> implements Entry<K, V> {
 78     private K key;
 79     private V value;
 80 
 81     public MapEntry(K key, V value) {
 82       this.key = key;
 83       this.value = value;
 84     }
 85 
 86     @Override
 87     public K getKey() {
 88       return key;
 89     }
 90 
 91     @Override
 92     public V getValue() {
 93       return value;
 94     }
 95 
 96     @Override
 97     public V setValue(V v) {
 98       V result = value;
 99       value = v;
100       return result;
101     }
102 
103     @Override
104     public int hashCode() {
105       return (key == null ? 0 : key.hashCode()) ^ (value == null ? 0 : value.hashCode());
106     }
107 
108     @Override
109     public boolean equals(Object o) {
110       if (!(o instanceof MapEntry)) {
111         return false;
112       }
113       MapEntry me = (MapEntry) o;
114       return (key == null ? me.getKey() == null : key.equals(me.getKey()))
115           && (value == null ? me.getValue() == null : value.equals(me.getValue()));
116     }
117 
118     @Override
119     public String toString() {
120       return key + "=" + value;
121     }
122   }
123 }