Java 32-Bit VS 64-Bit Compatibility

Java 32-bit vs 64-bit compatibility

Yes, Java bytecode (and source code) is platform independent, assuming you use platform independent libraries. 32 vs. 64 bit shouldn't matter.

JRE 32bit vs 64bit

64-bit vs. 32-bit really boils down to the size of object references, not the size of numbers.

In 32-bit mode, references are four bytes, allowing the JVM to uniquely address 2^32 bytes of memory. This is the reason 32-bit JVMs are limited to a maximum heap size of 4GB (in reality, the limit is smaller due to other JVM and OS overhead, and differs depending on the OS).

In 64-bit mode, references are (surprise) eight bytes, allowing the JVM to uniquely address 2^64 bytes of memory, which should be enough for anybody. JVM heap sizes (specified with -Xmx) in 64-bit mode can be huge.

But 64-bit mode comes with a cost: references are double the size, increasing memory consumption. This is why Oracle introduced "Compressed oops". With compressed oops enabled (which I believe is now the default), object references are shrunk to four bytes, with the caveat that the heap is limited to four billion objects (and 32GB Xmx). Compressed oops are not free: there is a small computational cost to achieve this big reduction in memory consumption.

As a personal preference, I always run the 64-bit JVM at home. The CPU is x64 capable, the OS is too, so I like the JVM to run in 64-bit mode as well.

Why should I use the 64-bit JDK over the 32-bit version?

No, for your development-time activities, 32 bits is likely to be enough.

The newest JVMs support pointer compression, but otherwise, the 64-bit version of an application requires more memory to run. Only use 64-bits if your application needs to address more memory (32 bits should address 4 Gb, but OS considerations sometimes make this less).

Besides wasting a bit of memory, a 64-bit version shouldn't be a problem, but anecdotally, all of the inexplicable crashes of the usually rock-solid JVM I hear complaints about are in 64-bit versions. It could be the OS or other factors, but if you don't have a reason for 64 bits, why push your luck?

How can I tell if a program I write is 32 bit or 64 bit?

I wrote some programs in java, but I would like to know if they are 32 bit or 64 bit

Neither. Your Java program is not specifically 32-bit or 64-bit.

All java programs should run on every up-to-date Java implementation.

When you compile a java program, it's turned into Java bytecode, which is often independent of what platform you compile it on and what platform you run it on.

This question should answer some questions for you: Java 32-bit vs 64-bit compatibility

Although a 64-bit Java implementation might handle some 64-bit operations better, there should be no difference as to how the program behaves (assuming you aren't using libraries that require 64-bit implementations).

Can I run 64bit java program on a 32bit windows os

Yes, of course. A java program is an intermediate byte code and not platform dependant. There is no such thing like "64 bit java program". But the JVM which runs the java program is of course platform dependant. On a 32bit machine you have to use a 32bit JRE or JDK, and vice versa.

See also java-32-bit-vs-64-bit-compatibility

Can a .class file generated using a 32 bit java compiler be used on a 64 bit system with 64 bit JVM?

Yes. Java byte code is independent from 32/64/... bit systems.

That's the main purpose: the compiled code shall be executable on any system, just the virtual machine is compiled for a special system architecture.

How do I make 32 bit or 64 bit application?

There is one byte code regardless of whether it will be used for 32-bit or 64-bit.

This means you can use libraries which were compiled on 32-bit machines before there was any 64-bit JVM, on a 64-bit JVM.

64-bit JVMs can use more memory, but not as much as you might think as modern 64-bit JVM use Compressed Oops so that you can use 32-bit references for up to 32 GB of heap. (you can use more off heap memory as well)

Many 32-bit JVM on 32-bit OSes are limited to 1.2 to 1.5 GB of memory. On 64-bit OS this limit might be 2.5 to 3.5 GB depending on the OS. A 64-bit JVM on a 64-bit OS is practically limited to around 1 TB of memory but this limit could be lifted in future (and depends on the OS)

The only difference you can have is if you use a JNI. A JNI shared library is dependant either a 32-bit or 64-bit library and you might only have one (in which case you ca only load it on a JVM of the same bit-ness) or it might behave differently.

Does Java 64 bit perform better than the 32-bit version?

Define your workload and what "perform" means to you.

This is sort of a running annoyance to me, as a performance geek of long standing. Whether or not a particular change "performs better" or not is dependent, first and foremost, on the workload, ie, what you're asking the program to do.

64 bit Java will often perform better on things with heavy computation loads. Java programs, classically, have heavy I/O loads and heavy network loads; 64 bit vs 32 bit may not matter, but operating systems usually do.

How can I tell if a jar was compiled on a 64bit or 32bit system?

Java bytecode is java bytecode, it doesn't matter whether it was built with a 32-bit or 64-bit JDK and there is no way to figure this out.

I think it does not make any difference to have a jar compiled with 32-bit or 64-bit. It should be machine-independent; unless you have some native library dependency or the java code is directly being compiled to native code.

32-bit or 64-bit application on 64-bit OS?

check this 64 bit java

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