java 自己实现的简单Map

如上一篇文章，做一个小记录，也是thinkinginjava中的一道练习题，嚯嚯，学习是一个循序渐进的过程

package com.lsw.first;

import java.util.HashSet;
import java.util.LinkedList;
import java.util.ListIterator;
import java.util.Set;

@SuppressWarnings("unchecked")
public class SimpleHashMap<K, V> {
	
	private static final int ARRAY_SiZE = 997;
	private LinkedList<MapEntry<K, V>>[] buckets = new LinkedList[ARRAY_SiZE];
	public V put(K key, V value) {	//添加一个键值对
		V oldValue = null;
		int index = Math.abs(key.hashCode()) % ARRAY_SiZE; //通过哈希码取绝对值再取模操作得到key的索引值
		if(buckets[index] == null) {
			buckets[index] = new LinkedList<MapEntry<K, V>>();
		}
		LinkedList bucket = buckets[index];
		MapEntry newEntry = new MapEntry<K, V>(key, value);
		ListIterator<MapEntry<K, V>> itr = bucket.listIterator();
		while(itr.hasNext()) {	//遍历，是否key已存在
			MapEntry<K, V> entry = itr.next();
			if(entry.getKey().equals(key)) {	//存在
				oldValue = entry.getValue();
				itr.set(newEntry);	//将新值覆盖旧值
				return oldValue;
			}
		}
		bucket.add(newEntry);//添加新键值对
		return oldValue;
	}
	
	public V get(Object key) {	//通过key得到value
		int index = Math.abs(key.hashCode()) % ARRAY_SiZE;	//通过哈希码取绝对值再取模操作得到key的索引值
		if(buckets[index] == null) {
			return null;
		}
		for(MapEntry<K ,V> entry : buckets[index]) {
			if(entry.getKey().equals(key)) {
				return entry.getValue();
			}
		}
		return null;
	}
	
	public Set<MapEntry<K, V>> entrySet() {	//返回一个set
		Set<MapEntry<K, V>> set = new HashSet<MapEntry<K, V>>();
		for(LinkedList<MapEntry<K, V>> bucket : buckets) {	//遍历数组以及LinkedList，将所有存在的键值对放进set中返回
			if(bucket == null) continue;
			for(MapEntry<K, V> entry : bucket) {
				set.add(entry);
			}
		}
		return set;
	}
	
	public V remove(Object key) {	//移除指定的键值对，并返回value
		V oldValue = null;
		int index = Math.abs(key.hashCode()) % ARRAY_SiZE;
		if(buckets[index] == null) {
			return null;
		}
		for(MapEntry<K, V> entry : buckets[index]) {
			if(entry.getKey().equals(key)) {
				oldValue = entry.getValue();
				buckets[index].remove(entry);
				return oldValue;
			}
		}
		return oldValue;
	}
	
	public void clear() {	//清除整个map
		for(int i = 0; i < buckets.length; i++) {
			if(buckets[i] != null) {
				buckets[i] = null;
			}
		}
	}
	
	static class MapEntry<K, V>{
		K key;
		V value;
		public MapEntry(K key, V value) {
			this.key = key;
			this.value = value;
		}

		public K getKey() {
			return key;
		}

		public V getValue() {
			return value;
		}

		public V setValue(V value) {
			V old = this.value;
			this.value = value;
			return old;
		}

		@Override
		public int hashCode() {
			return key == null ? 0 : key.hashCode()
					^ (value == null ? 0 : value.hashCode());
		}

		@Override
		public boolean equals(Object o) {
			if (!(o instanceof MapEntry)) {
				return false;
			}
			MapEntry<K, V> me = (MapEntry<K, V>) o;
			return (key == null ? me.getKey() == null : key.equals(me.getKey()))
					&& (value == null ? me.getValue() == null : value.equals(me
							.getValue()));
		}

		@Override
		public String toString() {
			return key + "=" + value;
		}
	}
}