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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?

Mishax
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  • 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: http://stackoverflow.com/questions/2506969/what-are-the-differences-in-jit-between-java-and-net – Crollster Apr 10 '13 at 09:59

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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.

toomasr
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  • I have done performance benchmarking on Excelsior JET. The compiled native code is significantly slower than what ever the Oracle JIT produces, in my tests it was 2x slower. It was even slower before the JIT optimized the code. – Emily L. Jan 26 '16 at 14:16
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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

Community
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Crollster
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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:

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:

Note: jaotc is not as simple to use as the OpenJ9 shared classes flag.

Alex
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