LRU算法

public class LRU<K, V> {

/**
* @param args
*/
public static void main(String[] args) {
// TODO Auto-generated method stub
lru();
}
static   void lru() {
        System.out.println();
        System.out.println("===========================LRU 链表实现===========================");
        LRU<Integer, String> lru = new LRU(5);
        lru.put(1, "11");
        lru.put(2, "12");
        lru.put(3, "13");
        lru.put(4, "11");
        lru.put(5, "14");
        System.out.println(lru.toString());
        lru.put(6, "66");
        System.out.println(lru.toString());
        lru.get(2);
        System.out.println(lru.toString());
        lru.put(7, "77");
        System.out.println(lru.toString());
        lru.get(4);
        System.out.println(lru.toString());
        System.out.println();
    }
private final  int MAX_CACHE_SIZE; 
private Entry head;
private Entry last;
private  HashMap<K,Entry<K,V>> hashMap;
//初始化
public LRU(int size){
this.MAX_CACHE_SIZE = size;
hashMap = new HashMap<>();
}
//存放数据
public void put(K key,V value){
Entry entry = hashMap.get(key);
if(entry == null){//新的
if(hashMap.size()>=MAX_CACHE_SIZE){
//移除最后一个元素
hashMap.remove(last.key);
removeLast();
}
entry = new Entry();
            entry.key = key;
}
entry.value = value;
//放在第一个位置
putFirst(entry);
hashMap.put(key, entry);
}
public V get(K key){
Entry entry =  hashMap.get(key);
if(entry==null) return null;
putFirst(entry);
return (V) entry.value;
}
public void remove(K key){
Entry entry = hashMap.get(key);
       if (entry != null) {
           if (entry.pre != null) entry.pre.next = entry.next;
           if (entry.next != null) entry.next.pre = entry.pre;
           if (entry == head) head = entry.next;
           if (entry == last) last = entry.pre;
       }
       hashMap.remove(key);
}
private void putFirst(Entry entry) {
// TODO Auto-generated method stub
if (entry == head) return;
//中间的节点操作
if (entry.pre != null) entry.pre.next = entry.next;
   if (entry.next != null) entry.next.pre = entry.pre;
   if (entry == last) last = last.pre;
   if (head == null || last == null) {
            head = last = entry;
            return;
        }
   entry.next = head;
   head.pre = entry;
   head = entry;
   entry.pre = null;
}
//
private void removeLast() {
// TODO Auto-generated method stub
if(last!=null){
last = last.pre;
if(last==null) head = null;
else last.next = null;
}
}
  @Override
   public String toString() {
       StringBuilder sb = new StringBuilder();
       Entry entry = head;
       while (entry != null) {
           sb.append(String.format("%s:%s ", entry.key, entry.value));
           entry = entry.next;
       }
       return sb.toString();
   }
//内部类
 class Entry<K, V> {
       public Entry pre;
       public Entry next;
       public K key;
       public V value;
   }
}