lru算法

package lru;


import java.util.HashMap;
import java.util.LinkedHashMap;

public class LRUCache {
    private Node head;
    private Node end;
    private int limit; //缓存存储上限

    private HashMap<String, Node> hashMap;

    public LRUCache(int limit) {
        this.limit = limit;
        hashMap = new HashMap<String, Node>();
    }

    public String get(String key) {
        Node node = hashMap.get(key);
        if (node == null)
            return null;
        refreshNode(node);
        return node.value;
    }

    public void put(String key, String value){
        Node node = hashMap.get(key);
        if (node == null){
            if (hashMap.size() >= limit){
                String oldKey = removeNode(head);
                hashMap.remove(oldKey);
            }
            node = new Node(key,value);
            addNode(node);
            hashMap.put(key,node);
        }else{
            node.value = value;
            refreshNode(node);
        }
    }

    //删除节点
    public void remove(String key){
        Node node = hashMap.get(key);
        //先更新节点前后的指针域
        removeNode(node);
        //删除该节点
        hashMap.remove(key);
    }

    /**
     * 刷新被访问的节点位置
     * @param node
     */
    private void refreshNode(Node node) {
        //如果访问的是尾节点，无需移动节点；
        if (node == end){
            return;
        }
        //移除节点时，指针域的改变
        removeNode(node);
        //重新插入节点
        addNode(node);
    }

    private void addNode(Node node) {
    }

    /**
     * 删除节点时，指针域的改变；
     * @param node 要删除的节点
     */
    private String removeNode(Node node) {
        if (node == end){
            //尾节点移除
            end = end.pre;
        } else if (node == head){
            //头结点移除
            head = head.next;
        }else {
            node.pre.next = node.next;
            node.next.pre = node.pre;
        }
        return node.key;
    }
}

package lru;

public class Node {
    public Node   pre;
    public Node   next;
    public String key;
    public String value;

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