Friday, June 19, 2015

64-bit java -- my own mini Q&A

Q: will 32-bit java apps run in 64-bit JVM?
A: Write once, run anywhere. Sun was extremely careful during the creation of the first 64-bit Java port to insure Java binary and API compatibility, so all existing 100% pure Java programs would continue running just as they do under a 32-bit VM. However, non-pure java, like JNI, will break.
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Q: 32bit apps need recompilation?
A: Unlike pure java apps, all native binary code that was written for a 32-bit VM must be recompiled for use in a 64-bit VM. All currently supported operating systems do not allow the mixing of 32 and 64-bit binaries or libraries within a single process.

Q: The primary advantage of running Java in a 64-bit environment?
A: larger address space. This allows for a much larger Java heap size and an increased maximum number of Java Threads.

Q: complications?
A: Any JNI native code in the 32-bit SDK implementation that relied on the old sizes of these data types is likely to require updating.
%%A: if java calls another program, maybe that program will need to be 64-bit compatible. This answer is slightly relevant.

Q: how is 32/64 bit JDK's installed?
A: Solaris has both a 32 and 64-bit J2SE implementation contained within the same installation of Java, you can specify either version. If neither -d32 nor -d64 is specified, the default is to run in a 32-bit environment. All other platforms (Windows and Linux) contain separate 32 and 64-bit installation packages.

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New York (Time Square), NY, United States
http://www.linkedin.com/in/tanbin