public class LRUCache {        private int cacheSize;    private HashMap<Object, Entry> nodes;//缓存容器    private int currentSize;    private Entry first;//链表头    private Entry last;//链表尾    class Entry {        Entry prev;//前一节点        Entry next;//后一节点        int value;//值        int key;//键    }    public LRUCache(int capacity) {        currentSize = 0;        cacheSize = capacity;        nodes = new HashMap<Object, Entry>(capacity);//缓存容器    }        /**     * 获取缓存中对象,并把它放在最前面     */    public int get(int key) {        Entry node = nodes.get(key);        if (node != null) {            moveToHead(node);            return node.value;        } else {            return -1;        }    }        /**     * 添加 entry到hashtable, 并把entry      */    public void set(int key, int value) {        //先查看hashtable是否存在该entry, 如果存在，则只更新其value        Entry node = nodes.get(key);                if (node == null) {            //缓存容器是否已经超过大小.            if (currentSize >= cacheSize) {                nodes.remove(last.key);                removeLast();                } else {                currentSize++;            }                        node = new Entry();        }        node.value = value;        node.key=key;        //将最新使用的节点放到链表头，表示最新使用的.        moveToHead(node);        nodes.put(key, node);    }    /**     * 将entry删除, 注意：删除操作只有在cache满了才会被执行     */    public void remove(Object key) {        Entry node = nodes.get(key);        //在链表中删除        if (node != null) {            if (node.prev != null) {                node.prev.next = node.next;            }            if (node.next != null) {                node.next.prev = node.prev;            }            if (last == node)                last = node.prev;            if (first == node)                first = node.next;        }        //在hashtable中删除        nodes.remove(key);    }    /**     * 删除链表尾部节点，即使用最后 使用的entry     */    private void removeLast() {        //链表尾不为空,则将链表尾指向null. 删除连表尾（删除最少使用的缓存对象）        if (last != null) {            if (last.prev != null)                last.prev.next = null;            else                first = null;            last = last.prev;        }    }        /**     * 移动到链表头，表示这个节点是最新使用过的     */    private void moveToHead(Entry node) {        if (node == first)            return;        if (node.prev != null)            node.prev.next = node.next;        if (node.next != null)            node.next.prev = node.prev;        if (last == node)            last = node.prev;        if (first != null) {            node.next = first;            first.prev = node;        }        first = node;        node.prev = null;        if (last == null)            last = first;    }    /*     * 清空缓存     */    public void clear() {        first = null;        last = null;        currentSize = 0;    }}