A simple solution for LRUCache

LRUCache

import java.util.HashMap;

/**
 * Created by coxier on 17-3-10.
 */
public class LRUCache<K,V> {

    private final class Node {
        Node next;
        Node pre;
        K key;
        V value;

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

        public Node(){

        }
    }

    private HashMap<K, Node> nodeMap;
    private Node head;
    private Node tail;
    private int cap;

    public LRUCache(int capacity) {
        nodeMap = new HashMap<>(capacity);
        cap = capacity;
        head = new Node();
        tail = new Node();
        head.pre = null;
        head.next = tail;
        tail.next = null;
        tail.pre = head;
    }

    private void deleteNode(Node node) {
        Node next = node.next;
        Node pre = node.pre;
        next.pre = pre;
        pre.next = next;
    }

    private void addNodeToHead(Node node) {
        Node realHead = head.next;
        realHead.pre = node;
        head.next = node;
        node.next = realHead;
        node.pre = head;
    }

    public V get(K key) {
        Node node = nodeMap.get(key);
        if (node != null) {
            deleteNode(node);
            addNodeToHead(node);
            return node.value;
        }
        throw new IllegalArgumentException("No value match this key");
    }

    public void put(K key, V value) {
        Node node = nodeMap.get(key);
        if (node != null) {
            node.value = value;
            deleteNode(node);
            addNodeToHead(node);
            return;
        } else if (nodeMap.size() == cap) {
            nodeMap.remove(tail.pre.key);
            deleteNode(tail.pre);
        }
        node = new Node(key, value);
        addNodeToHead(node);
        nodeMap.put(key, node);
    }
}