Caching methodId and fieldId is fine: v2

java/rocksjni/portal.h

@@ -211,8 +211,7 @@ class WriteBatchJni {
 class HistogramDataJni {
  public:
   static jmethodID getConstructorMethodId(JNIEnv* env, jclass jclazz) {
-    jmethodID mid = env->GetMethodID(
-        jclazz, "<init>", "(DDDDD)V");
+    static jmethodID mid = env->GetMethodID(jclazz, "<init>", "(DDDDD)V");
     assert(mid != nullptr);
     return mid;
   }