Java 32-bit vs 64-bit compatibility

Question

Will Java code built and compiled against a 32-bit JDK into 32-bit byte code work in a 64-bit JVM   Or does a 64-bit JVM require 64-bit byte code   To give a little more detail  I have code that was working in a Solaris environment running a 32-bit JVM  but now I m getting issues after upgrading the JDK and Weblogic Server to 64-bit

User · Answer

All byte code is 8-bit based   That s why its called BYTE code  All the instructions are a multiple of 8-bits in size   We develop on 32-bit machines and run our servers with 64-bit JVM   Could you give some detail of the problem you are facing   Then we might have a chance of helping you  Otherwise we would just be guessing what the problem is you are having

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yo where wrong  To this theme i wrote an question to oracle  The answer was     If you compile your code on an 32 Bit Machine  your code should only run on an 32 Bit Processor  If you want to run your code on an 64 Bit JVM you have to compile your class Files on an 64 Bit Machine using an 64-Bit JDK

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Yes to the first question and no to the second question  it s a virtual machine  Your problems are probably related to unspecified changes in library implementation between versions  Although it could be  say  a race condition   There are some hoops the VM has to go through  Notably references are treated in class files as if they took the same space as ints on the stack  double and long take up two reference slots  For instance fields  there s some rearrangement the VM usually goes through anyway  This is all done  relatively  transparently   Also some 64-bit JVMs use  compressed oops   Because data is aligned to around every 8 or 16 bytes  three or four bits of the address are useless  although a  mark  bit may be stolen for some algorithms   This allows 32-bit address data  therefore using half as much bandwidth  and therefore faster  to use heap sizes of 35- or 36-bits on a 64-bit platform

User · Answer

Yes  Java bytecode  and source code  is platform independent  assuming you use platform independent libraries  32 vs  64 bit shouldn t matter

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I accidentally ran our  largeish  application on a 64bit VM rather than a 32bit VM and didn t notice until some external libraries  called by JNI  started failing   Data serialized on a 32bit platform was read in on the 64bit platform with no issues at all   What sort of issues are you getting  Do some things work and not others  Have you tried attaching JConsole etc and have a peak around   If you have a very big VM you may find that GC issues in 64 bit can affect you

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Unless you have native code  machine code compiled for a specific arcitechture  your code will run equally well in a 32-bit and 64-bit JVM   Note  however  that due to the larger adresses  32-bit is 4 bytes  64-bit is 8 bytes  a 64-bit JVM will require more memory than a 32-bit JVM for the same task

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The Java JNI requires OS libraries of the same  bittiness  as the JVM  If you attempt to build something that depends  for example  on IESHIMS DLL  lives in  ProgramFiles  Internet Explorer  you need to take the 32bit version when your JVM is 32bit  the 64bit version when your JVM is 64bit  Likewise for other platforms   Apart from that  you should be all set  The generated Java bytecode s b the same   Note that you should use 64bit Java compiler for larger projects because it can address more memory

User · Answer

Add a paramter as below in you in configuration while creating the exe  http   www technimi com index php do  group java forum building-an-exe-using-launch4j-for-32-bit-jvm   I hope it helps   thanks      jav

User · Answer

The 32-bit vs 64-bit difference does become more important when you are interfacing with native libraries  64-bit Java will not be able to interface with a 32-bit non-Java dll  via JNI

[java] Java 32-bit vs 64-bit compatibility

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