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diff --git a/src/java/native/JniConstants.h b/src/java/native/JniConstants.h
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+/*
+ * Copyright (C) 2010 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef JNI_CONSTANTS_H_included
+#define JNI_CONSTANTS_H_included
+
+#include <jni.h>
+
+/**
+ * A cache to avoid calling FindClass at runtime.
+ *
+ * Class lookup is relatively expensive (2.5us on passion-eng at the time of writing), so we do
+ * all such lookups eagerly at VM startup. This means that code that never uses, say,
+ * java.util.zip.Deflater still has to pay for the lookup, but it means that on a device the cost
+ * is definitely paid during boot and amortized. A central cache also removes the temptation to
+ * dynamically call FindClass rather than add a small cache to each file that needs one. Another
+ * cost is that each class cached here requires a global reference, though in practice we save
+ * enough by not having a global reference for each file that uses a class such as java.lang.String
+ * which is used in several files.
+ *
+ * FindClass is still called in a couple of situations: when throwing exceptions, and in some of
+ * the serialization code. The former is clearly not a performance case, and we're currently
+ * assuming that neither is the latter.
+ *
+ * TODO: similar arguments hold for field and method IDs; we should cache them centrally too.
+ */
+struct JniConstants {
+    static void init(JNIEnv* env);
+
+    static jclass inet6AddressClass;
+    static jclass inetAddressClass;
+    static jclass inetSocketAddressClass;
+    static jclass stringClass;
+};
+
+#define NATIVE_METHOD(className, functionName, signature) \
+    { #functionName, signature, reinterpret_cast<void*>(className ## _ ## functionName) }
+
+#endif  // JNI_CONSTANTS_H_included