public class LruCached {
    //node节点装载数据
    class Node<K, V> {
        K key;
        V value;
        Node pre;
        Node next;

        public Node() {
            this.pre = this.next = null;
        }

        public Node(K k, V v) {
            this.key = k;
            this.value = v;
            this.next = this.pre = null;
        }
    }

    //双向链表
    class DoubleLinkedList<K, V> {
        Node<K, V> head;
        Node<K, V> tail;

        public DoubleLinkedList() {
            this.head = new Node<>();
            this.tail = new Node<>();
            head.next = tail;
            tail.pre = head;
        }

        public void addHead(Node node) {
            node.next = head.next;
            node.pre = head;
            head.next.pre = node;
            head.next = node;
        }

        public void removeNode(Node node) {
            node.next.pre = node.pre;
            node.pre.next = node.next;
            node.pre = null;
            node.next = null;
        }

        public Node getLast() {
            return tail.pre;
        }
    }

    private int cacheSize;
    Map<Integer, Node<Integer, Integer>> map;
    DoubleLinkedList<Integer, Integer> doubleLinkedList;

    public LruCached(int cacheSize) {
        this.cacheSize = cacheSize;
        map = new HashMap<>();
        doubleLinkedList = new DoubleLinkedList<>();
    }

    public int get(int key) {
        if (!map.containsKey(key)) {
            return -1;
        }
        Node<Integer, Integer> node = map.get(key);
        doubleLinkedList.removeNode(node);
        doubleLinkedList.addHead(node);
        return node.value;
    }

    public void put(int key, int value) {
        if (map.containsKey(key)) {
            Node<Integer, Integer> node = map.get(key);
            node.value = value;
            map.put(key, node);
            doubleLinkedList.removeNode(node);
            doubleLinkedList.addHead(node);
        } else {
            if (map.size() == cacheSize) {
                Node<Integer, Integer> lastNode = doubleLinkedList.getLast();
                map.remove(lastNode.key);
                doubleLinkedList.removeNode(lastNode);
            }
            Node<Integer, Integer> newNode = new Node<>(key, value);
            map.put(key, newNode);
            doubleLinkedList.addHead(newNode);
        }
    }

    public static void main(String[] args) {
        LruCached lruCached = new LruCached(3);
        lruCached.put(1, 1);
        lruCached.put(2, 2);
        lruCached.put(3, 3);
        System.out.println(lruCached.map.keySet());
        lruCached.put(4, 4);
        System.out.println(lruCached.map.keySet());
        lruCached.put(5, 5);
        System.out.println(lruCached.map.keySet());
        lruCached.put(1, 1);
        System.out.println(lruCached.map.keySet());
    }
}

手写LRU(出自阳哥教学)