Merge pull request CyC2018#444 from kaykong/patch-1

Update 缓存.md

Author: CyC2018

notes/缓存.md

@@ -88,12 +88,14 @@ public class LRU<K, V> implements Iterable<K> {
 
     public void put(K key, V value) {
 
+        Node node;
         if (map.containsKey(key)) {
-            Node node = map.get(key);
+            node = map.get(key);
             unlink(node);
         }
-
-        Node node = new Node(key, value);
+        if (node == null) {
+            node = new Node(key, value);
+        }
         map.put(key, node);
         appendHead(node);
 
@@ -109,6 +111,9 @@ public class LRU<K, V> implements Iterable<K> {
         Node next = node.next;
         pre.next = next;
         next.pre = pre;
+        
+        node.pre = null;
+        node.next = null;
     }