Java实现简单哈希映射-优快云博客

本文介绍如何使用Java实现一个简单的哈希映射，包括插入、查找和获取操作。

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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