Android and C++: Necessary?

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+3 Q:

Android and C++: Necessary?

Just checking out Android development very superficially, and it seems that most everyone is working in Java. Yet

Android includes a set of C/C++ libraries used by various components of the Android system. These capabilities are exposed to developers through the Android application framework.

does this mean that, in Android applications, Java is used and C++ is used:

sometimes?
a lot?
almost never?
Never: you cannot use it for applications?

+2 A:

You could fork the Android platform and add more native code written in C++ or some other language, but code running on top of the Android platform uses Google's own p-code format which is created by conversion of Java class files.

Ben Voigt 2010-08-31 19:58:17

+5 A:

Sometimes. As least as possible, only for time-sensitive code, and even then it might not be a good solution. The standard way to make Android apps is Java.
This is because the Java code will truly be cross-platform and will work virtually across all devices. While the ndk is only supported for ARM processors as far as I know, and it's not entirely encouraged unless absolutely necessary.

A lot of people abuse the NDK to avoid using Java or the SDK. This is wrong.

Miguel Morales 2010-08-31 20:12:24

C++ is just as portable across platforms. It just needs an SDK and a compiler.

Martin York 2010-08-31 20:23:32

C++ is source portable, but the binary or compiled form is not.You'll need to compile your C++ code using the NDK and it targets only a few processors, mainly ARM.Because of this, C++ code is not as portable as Java code in Android applications. You'll currently only be able to use your C++ code with Android devices that have an ARM cpu.With Java, you wouldn't have to worry about this.

Miguel Morales 2010-08-31 20:34:55

I guess you could call Android Java code device-agnostic, but cross-platform it is not, since it won't run on anything except the Android platform.

Ben Voigt 2010-08-31 21:13:14

Perhaps the Android specific classes, the UI for sure won't run on other platform. But all other standard Java code most certainly will.Just like standard java code written for other platforms runs on Android.

Miguel Morales 2010-08-31 21:25:34

+4 A:

You can use c++ in your android app via the NDK. It must be used in conjuction with the Java-based SDK, and is designed only to be used for performance-critical pieces of code. It has more limited functionality than the SDK (can't display UI, etc.).

Reasins for using, from the docs:

The NDK will not benefit most applications. As a developer, you will need to balance its benefits against its drawbacks; notably, using native code does not result in an automatic performance increase, but does always increase application complexity. Typical good candidates for the NDK are self-contained, CPU-intensive operations that don't allocate much memory, such as signal processing, physics simulation, and so on. Simply re-coding a method to run in C usually does not result in a large performance increase. The NDK can, however, can be an effective way to reuse a large corpus of existing C/C++ code.

Thus, the majority of users will not use any C++ code.

Mayra 2010-08-31 20:18:14

Interestingly, my experience has been exactly the opposite: using native code DID provide a substantial automatic performance increase (to my surprise). This was pre-froyo though, so maybe things have changed now.

dbyrne 2010-08-31 20:44:41

Interesting, I haven't actually tried it myself.. Did the type of code you moved over fit their description of being CPU-intensive, without allocating much memory? I think the point is you can see increases if your code is CPU-bound, but if its memory bound, or IO-bound, then you aren't going to see much difference.

Mayra 2010-08-31 20:49:15

@dbyrne: Since the p-code will be converted to native on the fly it seems hard to believe. If you run it once fine. But the initial cost of compilation should happen once thus over a few thousand calls the difference will disappear. And if it is only once then you don't really gain much anyway.

Martin York 2010-08-31 22:07:56

@Mayra @Martin: It did fit the description of being CPU-bound without allocating a lot of memory. I did a straight translation from Java, and got about a 25-30% performance increase. The application is a fractal generator, and you can see the code in question here: http://github.com/dbyrne/Fractoid/blob/master/native-src/FractalMath/FractalMath.c

dbyrne 2010-09-01 13:54:56

@dbyrn: Then I wouldn't be suprised that you received a peformance gain. That sound like exactly the kind of app that would benefit, as the docs said. The point is if you take an a chunk of code at random and convert it to c++ you may not get any gains. You need to think about the kind of code you are writing, before deciding if it will benifit from being made native.

Mayra 2010-09-01 16:26:14

+2 A:

Underneath the covers most of the OS is C/C++.

http://developer.android.com/guide/basics/what-is-android.html
Anything in Green/Or red is written in C/C++.
Not sure about the Application Framework.

What is exposed to the application developer is done through the Java SDK (the first SDK provided). Though now a more limited (from what I have been told (I don;t have direct experience)) C++ SDK is available.

I suppose you could technically write everything in C++ but I have not seen any of documentation about how to access any of these components so in effect they are hidden behind the SDK and unless somebody reverse engineers how to get at them you will be stuck with what the SDK you use exposes.

Martin York 2010-08-31 20:20:12

"Most" is a little strong. There is C/C++ code for low-level things (kernel and core user space) and some parts that are performance critical or existing code (Skia, WebKit), but basically all of the application framework and apps are running under Dalvik.

hackbod 2010-08-31 23:01:10

I'll stick with most (I though it was a little weak actually). The parts you mention are in the Application Framework (which I don;t know about) but that is not really part of the OS (Its the application layer). ;-P

Martin York 2010-09-01 02:36:07

Well you are wrong. :p The window manager, process manager, package manager, all are written in Java. If you call that the framework, then an X11 server is not part of the OS either.

hackbod 2010-09-01 03:33:27

@hackbod: Is that not what I said already!

Martin York 2010-09-01 04:28:51

+1 A:

In my case, I use NDK to compile a shared, cross-platform C++ app core, and Java for the UI. The said core compiles and runs equally well on WinMobile and iPhone. The code division is about 60% core, 40% UI.

Seva Alekseyev 2010-08-31 20:28:54

+1 A:

Official Google's position is that developers must use Java as a main development platform, and use C++/NDK for time- and performance-sensitive operations. Also, the only supported APIs are Java ones. I.e. Google gives you only Java API and supports only Java API. Whatever you can find on the device in native world (any shared libraries, libc etc), can and may be changed by Google or device vendors at any time without notice and so you are discouraged to use your findings.

Practically standard libc functions work and probably will work all the time, but you should not rely on any device-specific libraries or lesser-known native libraries.

Eugene Mayevski 'EldoS Corp 2010-08-31 23:03:14

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Android and C++: Necessary?

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