diff --git a/src/main/java/com/leetcode/string/IsValidKuoHao.java b/src/main/java/com/leetcode/string/IsValidKuoHao.java
index 0fcf412..a98e52f 100644
--- a/src/main/java/com/leetcode/string/IsValidKuoHao.java
+++ b/src/main/java/com/leetcode/string/IsValidKuoHao.java
@@ -18,7 +18,13 @@ import java.util.Stack;
  */
 public class IsValidKuoHao {
 
-    private static Map<Character, Character> kuohao = new HashMap<Character, Character>() {{
+    private static Map<Character, Character> kuohao = new HashMap<Character, Character>() {
+        /**
+        *
+        */
+        private static final long serialVersionUID = 1L;
+
+        {
         put('(', ')');
         put('{', '}');
         put('[', ']');