Issue 1848 - Clean up local reference handling

jni/JniFilter.cpp

 /*
  * This file is part of Adblock Plus <https://adblockplus.org/>,
  * Copyright (C) 2006-2015 Eyeo GmbH
  *
  * Adblock Plus is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License version 3 as
  * published by the Free Software Foundation.
  *
  * Adblock Plus is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
@@ skipping 48 matching lines @@
     enumName = "ELEMHIDE_EXCEPTION";
     break;
   case AdblockPlus::Filter::TYPE_EXCEPTION:
     enumName = "EXCEPTION";
     break;
   default:
     enumName = "INVALID";
     break;
   }
 
-  jclass enumClass = env->FindClass(PKG("Filter$Type"));
-  jfieldID enumField = env->GetStaticFieldID(enumClass, enumName, TYP("Filter$Type"));
-  return env->GetStaticObjectField(enumClass, enumField);
+  JniLocalReference<jclass> enumClass(env, env->FindClass(PKG("Filter$Type")));
+  jfieldID enumField = env->GetStaticFieldID(*enumClass, enumName,
+      TYP("Filter$Type"));
+  return env->GetStaticObjectField(*enumClass, enumField);
 }
 
 static jboolean JNICALL JniIsListed(JNIEnv* env, jclass clazz, jlong ptr)
 {
   try
   {
     return GetFilterPtr(ptr)->IsListed() ? JNI_TRUE : JNI_FALSE;
   }
   CATCH_THROW_AND_RETURN(env, JNI_FALSE)
 }
@@ skipping 35 matching lines @@
   { (char*)"isListed", (char*)"(J)Z", (void*)JniIsListed },
   { (char*)"addToList", (char*)"(J)V", (void*)JniAddToList },
   { (char*)"removeFromList", (char*)"(J)V", (void*)JniRemoveFromList },
   { (char*)"operatorEquals", (char*)"(JJ)Z", (void*)JniOperatorEquals }
 };
 
 extern "C" JNIEXPORT void JNICALL Java_org_adblockplus_libadblockplus_Filter_registerNatives(JNIEnv *env, jclass clazz)
 {
   env->RegisterNatives(clazz, methods, sizeof(methods) / sizeof(methods[0]));
 }