LRU缓存 Java实现

class LRUCache {

	//实现双向链表
    class DLinkedNode {

        int key;
        int value;
        DLinkedNode pre;
        DLinkedNode next;

        public DLinkedNode(){}
        public DLinkedNode(int key, int value){
            this.key = key;
            this.value = value;
        }
    }

    Map<Integer, DLinkedNode> map;
    int capacity;
    DLinkedNode head, tail;

    public LRUCache(int capacity) {
        this.capacity = capacity;
        map = new HashMap<>();
        head = new DLinkedNode();
        tail = new DLinkedNode();
        head.next = tail;
        tail.pre = head;
    }
    
    public int get(int key) {
        DLinkedNode node = map.get(key);
        if (node == null) return -1;
        moveToHead(node);
        return node.value;
    }
    
    public void put(int key, int value) {
        DLinkedNode node = new DLinkedNode(key, value);
        DLinkedNode old = map.get(key);
        if (old == null) {
            if (map.size() == capacity){
                DLinkedNode T = removeTail();
                map.remove(T.key);
            }
        }
        else {
            removeNode(old);
        }
        addToHead(node);
        map.put(key, node);
    }

    private void moveToHead(DLinkedNode node) {
        removeNode(node);
        addToHead(node);
    }

    private void addToHead(DLinkedNode node) {
        head.next.pre = node;
        node.next = head.next;
        head.next = node;
        node.pre = head;
    }

    private DLinkedNode removeTail() {
        DLinkedNode node = tail.pre;
        removeNode(node);
        return node;
    }

    private void removeNode(DLinkedNode node) {
        node.pre.next = node.next;
        node.next.pre = node.pre;
    }
}

/**
 * Your LRUCache object will be instantiated and called as such:
 * LRUCache obj = new LRUCache(capacity);
 * int param_1 = obj.get(key);
 * obj.put(key,value);
 */