Gadgetory

hello my name is Gary sim from and with authority now Java is the official programming language of Android and Java is used not only on mobile but also on desktops and servers and Java is quite a unique programming language especially when compared to other programming languages like C there are some big differences that are easy to spot like C is not object orientated Java is object orientated however there's some key differences that affect the performance of programs written in C and program written in Java first of all Java programs are not compiled to machine code they are compiled to an intermediate code called bytecode Java bytecode and this Java bytecode is then executed on a Java Virtual Machine so to fulfill the goal of write once run anywhere a Java Virtual Machine can be implemented on Linux on windows on servers on Android and therefore the same bytecode the same intermediate code can be run on that platform without needing to be recompiled however that means that when the program runs it has to run through itself another program this virtual machine which of course uses CPU time uses memory and therefore that has an impact on the performance the other big difference is that Java uses automated memory management that means that if a program allocate some memory allocates an object the program it doesn't need to worry about when that object is no longer needed I think all the garbage collector will run periodically and collect up all the bits of memory that are no longer needed and discard them the problem is the garbage collector is an expensive thing to run for example if you're writing a game and you need to update the frames every 16 milliseconds having the garbage collector run right at the time when you're trying to update the frame will affect the performance of your app now C is quite different C compiled directly down to machine code if it's running on a desktop PC running an Intel chip it will compile directly to the Intel machine code if it's running on an ARM chip on a smartphone it will compile directly down to the machine code for the ARM chip and it doesn't have automated memory management if the program allocates memory is up to the programmer to free that memory at a time at the programmer field is the best so therefore generally considered that Java is slightly slower than C when the two are run side by side I thought would be interesting to see how that speed comparison looks on Android what is the speed difference between AC program and a Java program now normally Java programs are written using the SDK the software development kit and Google also release a thing called the NDK the native development kit which allows you to write C and C++ programs for Android so what I've done is I've written an app that uses both Java code and C code and implements the same functionality in both languages with an attempt to see how much longer it takes in one language compared to the other now the app does three things first of all it calculates the sha-1 hash of a block of data then it calculates the first million prime numbers using trial by division and then finally it runs a mathematical function that I wrote and it runs that a million times to see how long it takes now there are a couple of things I want to mention before we look at the actual results what first one is about optimization every software engineer knows that software should be optimized to run faster on each platform that it's being deployed to now while I was writing this code because I was looking at the how many nanoseconds it took to run each particular function because that was the idea of the benchmark I was quite surprised how drastically I could change the results by implementing a function one way or another now I've tried my best optimized the Java code and the C code so they give a fair test and if you want more details about the optimizations that I did in a comparison between the C code with Java code please get over to the Android ROM website and read the written article that goes along with this video it's also worth mentioning the Android Java virtual machines up to an including Android 4.4 KitKat Android used a java virtual machine code named dalvik and it was basically a java virtual machine that interpreted the bytecode and ran the appropriate instruction there and then on the processor it had a thing called just-in-time compiling which means that some sections of the code would be pre compiled into the native machine code and called upon where needed and that did give a boost to the performance of virtual machine however from Android 5.0 the default virtual machine became art the Android runtime now the Android runtime used ahead of time compiling which basically meant when a program was installed it was compiled at that moment in the background on to the processor for the processor of your particular machine probably an ARM processor though it could of course be an Intel processor and then with the advent of Android 6.0 what happened is that arm had been working in the background with Google to improve that compiling stage in that ahead of time compiler so that the machine code that was generated was even more efficient that was known as the optimizing compiler and we'll seeing the results how those three different Java virtual machines affect the performance of the Java programs running on phones I'd also like to point out they run this benchmark on both 32-bit and 64-bit processors and while that's important is because a lot of the code that's in my test app uses long integers now traditionally in C and Java an integer a whole number is 32 bits wide however there are things called long integers which are 64 bits wide now of course if you're running a java virtual machine on a 32-bit processor but you have a 64 bit number it has to do twice the work to process that number now actually it turns out that doing division or specifically the modulus operator for working out the remainder in Java on a 64-bit number is actually quite slow when running on a 32-bit machine and we'll see that again reflected in the code so what I did was I wrote this app and it runs these three tests in Java and in CA reports the relative difference in the time now but I've run this test over 21 different devices a big shout-out to my colleagues at handle Authority for helping me run this on a wide range of devices some are 32-bit some are 64-bit some have KitKat some have marshmallow some have lollipop ok and basically what I'm interested in is the difference in the speed between Java and C I'm not interested in the absolute time of course a modern-day snapdragon 820 processor is to be faster than a quad-core 32-bit processor from two years ago but on the same processor the Java and the C are both running it's the difference between that performances is interesting to us not the absolute speed now once I ran the tests what I actually found was that the result grouped together quite nicely you find that 32-bit lollipop all the results were grouped into one area 64-bit marshmallow those results were all grouped together so let's have a look at what I found out so the first test was to take a block of data and create a hash and sha-1 hash for that block of data and here are the results now again this is the relative difference the percentage difference between Java and C and the first thing we see is that Java is slower now in the worst case scenario which is on an Android 5 32 bit device it was three hundred percent 296 percent three hundred percent slow which is four times slower now as we go down through the different devices we find that next you find 64 bit Android 5 you find 32 bit Android 4.4 but the fastest of all of these was Android 6.0 running on a 64-bit processor so for a real-world application like creating cryptographic hashes we find that Java is actually 60% slower than C on the most modern 64-bit processors and in fact up to 4 times slower compared to C on older devices now the next test works out the first million primes by using trial by division now as I pointed out earlier I'm using 64-bit integers for this and 64-bit division on a 32-bit Java program is actually quite slow and we'll see that now in the results and the results here are quite amazing if we look at 32-bit Android marshmallow we see that Java is 263 percent slower than C we also find that 32-bit Android 5 and 32-bit Android 4.4 are significantly slow 172 % and 240 percent respectively however once we move over to 60 orbit because we're using those 64-bit integers we find Android 5.0 on a 64-bit process was only 38% slower and look at this Android 6.0 on a 64-bit processor is only 3% slower now that 3% difference is really quite amazing and that's a lot to do with the new Android runtime with ease ahead of time compiling and the optimizing compiler that went into Android 6.0 marshmallow now my third test runs a mathematical function that I invented it's my own invention just as some multiplications and some hailing as and deprovision both integer and floating-point and it comes up with a result at the end and that's run a million times to see how fast it runs on Java and C now again like the prime number testing here I'm using 64-bit integers and we can see the difference with a java virtual machine running 32-bit and 64-bit integers so looking at the worst results first here we find that Android 4.4 on a 32-bit machine is 384 percent slower Android 5.0 on a 32-bit machine is 259 percent slower and Android 6.0 on a 32-bit machine is in 191 percent slower now once again we move over to 64 bits we find that Android 5.0 on 64 bits is only 52 percent slower but here's the amazing thing Java running on an Android 6.0 machine on a 64-bit processor was actually faster than the C code now there could be a couple of reasons for this one is definitely the optimizing compiler maybe it found a better optimization than the C compiler did and therefore was able to create faster code and then when you run that a million times that difference is seen quite clearly and the other thing cause to remember is that what now using this simple mathematical function the garbage collector doesn't run at all it doesn't need to run because it's just doing math there isn't much memory allocation going on so what does all this mean well first of all the choice between Android and C actually isn't that black and white because when you're writing an Android you actually want to have access to the Android UI to the Android API to the various Android services including Google Play and all of those are only available via Java C is really only useful if you want to write a game engine or you've got some real heavy lifting to do and it will be quicker to do that in C now previously if you had that heavy lifting to do it might have been worthwhile porting sections of your code large sections of your code to C to get the performance gain however what my quick testing has shown is that that performance gap is reducing rapidly and in fact in some cases it looks now that Java is just as fast as or even faster than C well my name is Gary Simms from Android or thority I hope you enjoyed this video if you did please do give it a thumbs up also please don't forget to subscribe to and royal authority YouTube channel also you should download and install the Android authority app that will give you access to all the latest news and things that we are publishing also please don't forget to use the comments below to tell me what you think about Java what you think about say what you think of a hand with development in general it will be great to hear from you also if you want to please head over to the andrew authority forums you can use this link here and there you can ask me any questions you want about this video including about the app that I wrote including about C including about Java and I'll try and help you if I can and last of 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