LRU缓存实现(Java)

package practice;

import java.util.HashMap;
import java.util.Map;

/**
 *     链表头,链表尾,map,size
 *     构造方法:初始化size,构建map,头尾赋空,头尾相连
 *     get: 判断是否包含key -> 得到key的Node -> 删除node -> 把Node添加到头部 -> 返回node.v
 *     put: 判断是否存在key -> 存在,删除 -> 初始化新节点,put到map中,头插 -> 长度超出,移除尾节点
 */
public class LRUTest<K, V> {

    Node head;
    Node tail;
    Map<K, Node> map;
    int maxSize;

    private class Node {
        Node pre;
        Node next;
        K k;
        V v;

        public Node(K k, V v) {
            this.k = k;
            this.v = v;
        }
    }

    public LRUTest(int maxSize) {
        this.maxSize = maxSize;
        map = new HashMap<>(maxSize * 4 / 3);
        head = new Node(null, null);
        tail = new Node(null, null);
        head.next = tail;
        tail.pre = head;
    }

    public V get(K k) {
        if (!map.containsKey(k)) {
            return null;
        }
        Node node = map.get(k);
        unlink(node);
        appendHead(node);
        return node.v;
    }

    public void put(K k, V v) {
        if (map.containsKey(k)) {
            unlink(map.get(k));
        }
        //不存在
        Node node = new Node(k, v);
        appendHead(node);
        map.put(k, node);
        if (map.size() > maxSize) {
            //长度超出,移除尾节点
            K removeKey = removeTail();
            map.remove(removeKey);
        }
    }

    public void unlink(Node node) {
        Node pre = node.pre;
        Node next = node.next;
        pre.next = next;
        next.pre = pre;

        node.pre = null;
        node.next = null;
    }

    public void appendHead(Node node) {
        Node headNext = head.next;
        head.next = node;
        node.pre = head;

        node.next = headNext;
        headNext.pre = node;
    }

    public K removeTail() {
        Node node = tail.pre;
        Node pre = node.pre;

        pre.next = tail;
        tail.pre = pre;

        node.pre = null;
        node.next = null;

        return node.k;
    }
}

使用哈希表存储节点。降低查找复杂度