Is there any way to compile from Java to standalone (or library) machine code without requiring a JVM?
There used to be a tool called GCJ that was part of GCC, but it's been removed. Now, all the links in the GCC site re-direct to their non-GCJ equivalents.
NB: the comments all refered to my original answer saying you can compile Java to native code with GCJ.
Yes!
Oracle has been working on the GraalVm, which supports Native Images. Check here: https://www.graalvm.org/
Native Image
The native image feature with the GraalVM SDK helps improve the startup time of Java applications and gives them a smaller footprint. Effectively, it's converting bytecode that runs on the JVM (on any platform) to native code for a specific OS/platform — which is where the performance comes from. It's using aggressive ahead-of-time (AOT) optimizations to achieve good performance.
See more:
Summary
https://www.graalvm.org/docs/getting-started/#native-images
Demos: Native images for faster startup
https://www.graalvm.org/docs/examples/native-list-dir/
Detailed: 'Ahead-of-time Compilation'
https://www.graalvm.org/docs/reference-manual/aot-compilation/
The Micronaut platform uses GraalVM to make native microservices:
https://guides.micronaut.io/latest/micronaut-creating-first-graal-app.html
Excelsior JET is a commercial Java to native code compiler. However, it was discontinued in May 2019.
Yes, the JIT in the JVM does exactly that for you.
In fact it can produce faster code than compiling the code in advance as it can generate code optimised for the specific platform based on how the code is used at runtime.
The JVM is always involved even if a very high percentage is compiled to native code as you could load and run byte code dynamically.
Another possibility would be RoboVM.
However, it only seems to work on Linux, iOS and Mac OS X.
As of today, the project still seems somewhat alive contrary to some posts online claiming the project to be dead.
Related
I've recently been experimenting with Processing (https://processing.org/).
It's a sort of IDE used to make GUI design in Java easier. Since I'm not a fan of swing or AWT, I found it quite fun to use.
Something interesting to note though. When I "export" the Application for windows, it creates both a 32-bit and 64-bit version.
I'm a little confused as I thought after Java source code is compiled to Java bytecode, it can be run anywhere as long as that place as a JVM. (Write once, run anywhere).
So why are both a 32 bit and 64 bit version of the app created? Shouldn't the bytecode be platform independent and only be translated using Just-In-Time compilation to whichever architecture the JVM is on, during runtime? At least, I know that's how .NET does it with the CLR.
I'm going to attempt to answer my own question by saying since the applications created are .exe files, the translation to native architecture happened ALREADY, since windows was specified as a target-platform...I guess to increase efficiency?
Otherwise, I'm confused. The only time I've seen a compilation happen twice is when I was programming C++, and needed to compile twice for 32-bit and 64-bit.
Thank you!
Processing is built on top of JOGL which is (basically) a Java wrapper of OpenGL, which is a device-specific graphics library.
Also, Processing (can) include a whole JVM with its exported applications, so end users don't have to worry about downloading Java. The JVM itself is OS-dependent, so the exported application is as well.
You can confirm this by taking a look at the files that Processing creates. Specifically, notice these files:
jogl-rt-natives-windows-amd64.jar
jogl-all-natives-windows-amd64.jar
These .jar files contain the native files required by JOGL.
I have simple java programm that will just print Hello World.Can it be possible to print without using JVM installed in a machine ?But compiler is there.
You can compile Java Byte Code to Machine Code using something like this:
http://en.wikipedia.org/wiki/GNU_Compiler_for_Java
Or you can use any of the MANY Java to C/C++ converters out there to make a C/C++ version, and compile that. (Search Google for "Java C Converter")
Warning: I have never tried any of these, including the linked GNU Compiler, so I cannot make any attestations to their usefulness or quality.
#SplinterReality already pointed you to some compilers (googling "java bytecode to native code compiler" will show you some more options).
I will just expand on that seeing some people are a bit confused:
The JVM is a program that takes java bytecode, which you get by running javac on your java source code (or you generate it in some other fashion). Bytecode is just a set of instructions that the JVM understands, it's there to give you a consistent set of opcodes which are platform independent. It's the JVM's job to then map those opcodes to native instructions, that's why JVMs are platform dependent. That's why when you compile your java source code to java bytecode you can run it on every platform.
That's why, whether you have java source or bytecode, you can take it and just compile it directly to native code (platform dependent, actually sometimes that's exactly what the JVM, and to be more precise the JIT, does - it compiles stuff to native code when it sees the need to). Still there's more to the JVM than just bytecode interpretation - for instance you need to take care of garbage collection.
So the answer is: yes, but do you really want to do it? Unless you want to be running it on some embedded systems I don't really see any reason to.
Yees, it is possible to run a java program without a JVM, albeit with limitations. Aside from the http://en.wikipedia.org/wiki/GNU_Compiler_for_Java , there is the GraalVM native-image generator, which could be used : https://www.graalvm.org.
If that program is a one file source code (not compiled in bytecode) then you can ;)
Here or here. Here will be fine as well ;)
Just put it there and press compile and run.
But it will work only with simple stuff only, and you have to have source code.
I would not be surprised if there would be a site that would allowed to upload class from users PC
I was recently comparing the JVM and CLR platforms and was discussing the impact of JIT compilation. The discussion I was having led to .NET's ability to precompile code using the NGen tool, which would eliminate the need for JIT compilation. Is there an equivalent in the Java platform?
The native compiler that I've heard the most about is Excelsior JET - Java Virtual Machine and Native Compiler. See http://www.excelsior-usa.com/jet.html for more details. Basically you can turn your project into a single executable without the hassles of the usual Java packaging.
They have been around for a long time (they where here when I joined the Java ranks in 2001 and they are here now. I just heard a week ago how a company is using their solution are and are happy with it.
About couple of years ago at JavaONE I also met a developer or two of the product and they told me that they are live and kicking and doing well.
I'm not aware of any, personally (you can look at options like launch4j, jexe, etc, they are just wrappers, not like NGen), and I'm not sure how feasible it would be... The answer to this question goes into some details on the subject of compiling to native code: Differences in JIT between Java and .Net
Yes. As of Java 9, you can. The feature you are looking for is called Ahead of Time (AOT) compilation.
There are two main JVMs in use today:
HotSpot (and it's variants), which is the main JVM from Oracle.
OpenJ9, originally from IBM.
OpenJ9
In OpenJ9, just run the Java Virtual Machine with the -Xshareclasses:persistent option. This causes the VM to store compiled binaries into a cache, which persists across system boots. It does not force the Java VM to use the precompiled code in all cases, as in many cases Just In Time (JIT) code can execute faster. The JVM will pick whether to use the cached binary or not on a case by case basis. When a cached AOT method is run it might also be optimized further by the Just-In-Time (JIT) compiler.
Full details are available at:
https://www.eclipse.org/openj9/docs/aot/
https://www.eclipse.org/openj9/docs/xshareclasses
HotSpot (OpenJDK)
The HotSpot (OpenJDK) builds now include an experimental VM that can completely precompile everything, called GraalVM. You manually create native binaries using the jaotc executable. Note: this is currently only available on Linux (and possibly Mac) systems.
Details on how to use the jaotc compiler are at:
https://docs.oracle.com/javase/10/vm/java-hotspot-virtual-machine-performance-enhancements.htm#JSJVM-GUID-F33D8BD0-5C4A-4CE8-8259-FD9D73C7C7C6
https://openjdk.java.net/jeps/295 (this includes an example where you generate and use an AOT library for the java.base module).
Note: jaotc is not as simple to use as the OpenJ9 shared classes flag.
I need to use Java for a desktop application. I heard that there are many tools that compile java natively, is this true? does these tools compile java program into machine code?
THank you!
Since the (Sun/Oracle) Java VM has a good JIT (just-in-time) compiler, you don't have to compile your Java program to machine code yourself. The compiler will do that on the fly when it's necessary.
So: Speed up your Java programs just as every other program:
reduce algorithmic complexity
exploit parallelism
compute at the right moment
find and remove bottlenecks
...
Since Java is a garbage collected language, there is one important point to more speed: reduce allocations! Reducing allocations will help you at least twice: The allocation itself isn't done and the garbage collector will have to do less work (which will save time).
I agree with the others that compiling to machine code does not make much sense: mind that C free/malloc have same or higher costs than Java new/garbage collection.
The NetBeans IDE comes with a built-in Profiler; so you could profile your application in that IDE to find bottlenecks.
are you coding the app or it's someone's else?
It looks you're trying to run an java app that is slow. Try increasing the memory when running it. You can change the shell script specifying these params:
java -Xms64m -Xmx512m
I need to use Java for a desktop application. I heard that there are
many tools that compile java natively, is this true? does these tools
compile java program into machine code?
Such programs do exist, but may come with tradeoffs when using some of the more dynamic capabilities of the Java platform like you may lose the ability to load new classes at runtime. The JVM may have a slow start up, but it's plenty fast enough once it gets going.
That said, one solution that I didn't see anyone mention here is to replace code written in Swing with SWT. The SWT toolkit uses native code underneath.
I want to download a JIT compiler for Java. Where can I get a good JIT compiler?
The JIT compiler runs as part as the JVM - it's not something you download and run separately.
In the early days of Java, you used to be able to run a JIT as a plugin - but these days there's no need. Any mainstream, modern desktop Java environment will include a JIT.
Most of the JVMs have a JIT built in. Download any of them.
My guess is you are looking for a java to native .exe compiler in the mistaken belief that this will yield a significant performance difference. For Java this is not the case for most real applications and just makes deploying them harder.
Any modern well-performing Java implementation comes with a JIT, and normally you do not have to worry about these kind of things. The most frequent is the Oracle Java implementation available from http://java.com.
If you, however, have a performance problem it is usually a problem with your own code, so use a suitable profiler (jvisualvm in the Sun 6 JDK is a good, free starting point) to identify your bottlenecks, so you can correct them.