Java实现简单哈希映射-优快云博客

来自Thinking In Java【P493】。

       Java Code  
    

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package org.vocano.java.tst;

import java.util.*;

public class SimpleHashMap<K,V> extends AbstractMap<K,V> {
     // Choose a prime number for the hash table
     // size, to achieve a uniform distribution:
     static final int SIZE = 997;
     // You can't have a physical array of generics,
     // but you can upcast to one:
    @SuppressWarnings( "unchecked")
    LinkedList<SimpleEntry<K,V>>[] buckets =
         new LinkedList[SIZE];
     public V put(K key, V value) {
        V oldValue = null;
         int index = Math.abs(key.hashCode()) % SIZE;
         if(buckets[index] == null)
            buckets[index] = new LinkedList<SimpleEntry<K,V>>();
        LinkedList<SimpleEntry<K,V>> bucket = buckets[index];
        SimpleEntry<K,V> pair = new SimpleEntry<K,V>(key, value);
         boolean found = false;
        ListIterator<SimpleEntry<K,V>> it = bucket.listIterator();
         while(it.hasNext()) {
            SimpleEntry<K,V> iPair = it.next();
             if(iPair.getKey().equals(key)) {
                oldValue = iPair.getValue();
                it.set(pair); // Replace old with new
                found = true;
                 break;
            }
        }
         if(!found)
            buckets[index].add(pair);
         return oldValue;
    }
     public V get(Object key) {
         int index = Math.abs(key.hashCode()) % SIZE;
         if(buckets[index] == null) return null;
         for(SimpleEntry<K,V> iPair : buckets[index])
             if(iPair.getKey().equals(key))
                 return iPair.getValue();
         return null;
    }
     public Set<Map.Entry<K,V>> entrySet() {
        Set<Map.Entry<K,V>> set= new HashSet<Map.Entry<K,V>>();
         for(LinkedList<SimpleEntry<K,V>> bucket : buckets) {
             if(bucket == null) continue;
             for(SimpleEntry<K,V> mpair : bucket)
                set.add(mpair);
        }
         return set;
    }
     public static void main( String[] args) {
        SimpleHashMap< String, String> m =
             new SimpleHashMap< String, String>();
        m.put( "a", "b");
        System.out.println(m.get( "a"));
    }
}

hashmap的简单实现