手写LRU(出自阳哥教学)

public class LruCached<K, V> {
    class Node<K, V> {
        K key;
        V value;
        Node<K, V> pre;
        Node<K, V> next;

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

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

    class DoubleLinkedList<K, V> {
        Node head;
        Node tail;

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


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

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

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

    Map<K, Node<K, V>> map = null;
    DoubleLinkedList doubleLinkedList = null;
    int cacheSize;

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

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

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

    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());
    }
}