diff --git a/app/src/main/jni/librime_jni/jni-utils.h b/app/src/main/jni/librime_jni/jni-utils.h
index 8cb4519f09..a078999aca 100644
--- a/app/src/main/jni/librime_jni/jni-utils.h
+++ b/app/src/main/jni/librime_jni/jni-utils.h
@@ -1,15 +1,9 @@
 /*
- * SPDX-FileCopyrightText: 2024 Rime community
+ * SPDX-FileCopyrightText: 2015 - 2025 Rime community
  *
  * SPDX-License-Identifier: GPL-3.0-or-later
  */
-
-// SPDX-FileCopyrightText: 2015 - 2024 Rime community
-//
-// SPDX-License-Identifier: GPL-3.0-or-later
-
-#ifndef TRIME_JNI_UTILS_H
-#define TRIME_JNI_UTILS_H
+#pragma once
 
 #include <jni.h>
 #include <utf8.h>
@@ -22,12 +16,6 @@ static inline void throwJavaException(JNIEnv *env, const char *msg) {
   env->DeleteLocalRef(c);
 }
 
-static inline jint extract_int(JNIEnv *env, jobject f) {
-  return env->CallIntMethod(
-      f,
-      env->GetMethodID(env->FindClass("java/lang/Integer"), "intValue", "()I"));
-}
-
 class CString {
  private:
   JNIEnv *env_;
@@ -89,28 +77,12 @@ class JString {
   jstring operator*() { return jstring_; }
 };
 
-class JClass {
- private:
-  JNIEnv *env_;
-  jclass jclass_;
-
- public:
-  JClass(JNIEnv *env, const char *name)
-      : env_(env), jclass_(env->FindClass(name)) {}
-
-  ~JClass() { env_->DeleteLocalRef(jclass_); }
-
-  operator jclass() { return jclass_; }
-
-  jclass operator*() { return jclass_; }
-};
-
 class JEnv {
  private:
-  JNIEnv *env;
+  JNIEnv *env = nullptr;
 
  public:
-  JEnv(JavaVM *jvm) {
+  explicit JEnv(JavaVM *jvm) {
     if (jvm->GetEnv(reinterpret_cast<void **>(&env), JNI_VERSION_1_6) ==
         JNI_EDETACHED) {
       jvm->AttachCurrentThread(&env, nullptr);
@@ -136,18 +108,6 @@ class GlobalRefSingleton {
   jclass Boolean;
   jmethodID BooleanInit;
 
-  jclass HashMap;
-  jmethodID HashMapInit;
-  jmethodID HashMapPut;
-
-  jclass ArrayList;
-  jmethodID ArrayListInit;
-  jmethodID ArrayListAdd;
-
-  jclass Pair;
-  jmethodID PairFirst;
-  jmethodID PairSecond;
-
   jclass Rime;
   jmethodID HandleRimeMessage;
 
@@ -180,7 +140,7 @@ class GlobalRefSingleton {
   jclass KeyEvent;
   jmethodID KeyEventInit;
 
-  GlobalRefSingleton(JavaVM *jvm_) : jvm(jvm_) {
+  explicit GlobalRefSingleton(JavaVM *jvm_) : jvm(jvm_) {
     JNIEnv *env;
     jvm->AttachCurrentThread(&env, nullptr);
 
@@ -198,23 +158,6 @@ class GlobalRefSingleton {
         env->NewGlobalRef(env->FindClass("java/lang/Boolean")));
     BooleanInit = env->GetMethodID(Boolean, "<init>", "(Z)V");
 
-    HashMap = reinterpret_cast<jclass>(
-        env->NewGlobalRef(env->FindClass("java/util/HashMap")));
-    HashMapInit = env->GetMethodID(HashMap, "<init>", "()V");
-    HashMapPut = env->GetMethodID(
-        HashMap, "put",
-        "(Ljava/lang/Object;Ljava/lang/Object;)Ljava/lang/Object;");
-
-    ArrayList = reinterpret_cast<jclass>(
-        env->NewGlobalRef(env->FindClass("java/util/ArrayList")));
-    ArrayListInit = env->GetMethodID(ArrayList, "<init>", "(I)V");
-    ArrayListAdd = env->GetMethodID(ArrayList, "add", "(ILjava/lang/Object;)V");
-
-    Pair = reinterpret_cast<jclass>(
-        env->NewGlobalRef(env->FindClass("kotlin/Pair")));
-    PairFirst = env->GetMethodID(Pair, "getFirst", "()Ljava/lang/Object;");
-    PairSecond = env->GetMethodID(Pair, "getSecond", "()Ljava/lang/Object;");
-
     Rime = reinterpret_cast<jclass>(
         env->NewGlobalRef(env->FindClass("com/osfans/trime/core/Rime")));
     HandleRimeMessage = env->GetStaticMethodID(Rime, "handleRimeMessage",
@@ -277,9 +220,7 @@ class GlobalRefSingleton {
         env->GetMethodID(KeyEvent, "<init>", "(IILjava/lang/String;)V");
   }
 
-  const JEnv AttachEnv() const { return JEnv(jvm); }
+  [[nodiscard]] JEnv AttachEnv() const { return JEnv(jvm); }
 };
 
 extern GlobalRefSingleton *GlobalRef;
-
-#endif  // TRIME_JNI_UTILS_H