Add AutoJObject and AutoGlobalJObject

base/android/auto_jobject.h

Index: base/android/auto_jobject.h
diff --git a/base/android/auto_jobject.h b/base/android/auto_jobject.h
new file mode 100644
index 0000000000000000000000000000000000000000..a4f3c38adaed70cae8d28b5bd38420b8dab7eee4
--- /dev/null
+++ b/base/android/auto_jobject.h
@@ -0,0 +1,43 @@
+// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef BASE_ANDROID_AUTO_JOBJECT_H_
+#define BASE_ANDROID_AUTO_JOBJECT_H_
+
+#include <jni.h>
+
+namespace base {
+namespace android {
+
+// Holds a local reference to a Java object. The global reference is scoped
+// to the lifetime of this object.
+class AutoJObject {
+ public:
+  // Assumes that obj is a local reference to a Java object and takes ownership
+  // of this local reference. The local /reference is deleted when this object
+  // goes out of scope.
+  AutoJObject(JNIEnv* env, jobject obj);
+  // Takes a new local reference to the Java object held by other. The local
+  // reference is deleted when this object goes out of scope.
+  AutoJObject(const AutoJObject& other);
+  ~AutoJObject();
+
+  inline JNIEnv* env() const { return env_; }

[brettw, 2011/08/02 15:55:39]

We wouldn't normally write "inline" here. C++ says all functions in headers will
be inline anyway.

+  inline jobject obj() const { return obj_; }
+  // Releases the local reference to the caller. The caller *must* delete the
+  // local reference when it is done with it.
+  jobject Release();
+
+ private:
+  AutoJObject();  // Not permitted.

[brettw, 2011/08/02 15:55:39]

If you're returning by value, not permitting the default constructor also seems
like a mistake since it permits things like this:

AutoJObject foo;
if (bar) {
  for = DoSomething();
}

Basically, if you need your object to do any of these things (which is
discouraged), it's usually best to have it do all of them to match user's
expectations.

+  void operator=(const AutoJObject&);  // DISALLOW_ASSIGN
+
+  JNIEnv* env_;
+  jobject obj_;
+};
+
+}  // namespace android
+}  // namespace base
+
+#endif  // BASE_ANDROID_AUTO_JOBJECT_H_