java 自己实现的简单Map

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;
}
}
}