Differences of JDK x86 and JDK x64

Question

Dear all,
I am in the progress on studying Java update with existing program.
For previous, the program is complied in eclipse under JDK 1.4.2.
We are now updating the JRE and JDK 1.6 update 30, however, there are several questions. Most appreciated if any one can provide a direction or guidance on it.
1. As my understanding, Java should be able to compile and run under x86 and x64 platform, and it should be no difference on the compiled classes. The only difference should be x86 JVM and x64 JVM (for example, x86 JVM has better than x64 JVM, and x64 JVM should be support larger address range than x86 JVM). If not, what will be differences among classes compiled under x86 and that of x64?
2. The x86 classes can be executed under x64 JVM. Can the x64 classes be executed under x86 JVM? Although, the classes will be read into byte stream into VM...
3. If we need the x64 classes to execute under x86 environment, what should we do? If the x64 classes cannot be run in x86 JVM.

Answer 1

929805 wrote:
Is there documentation or reference (e.g. Java Knowledge Base, etc) stating this issue?There is documentation which states how Java compiled code must be handled within a JVM. (The Java Virtual Machine Specification.) Here's a quote from very close to the beginning:
The Java virtual machine is an abstract machine.So you shouldn't expect it to mention specific machine architectures, or to specify how it should work on any particular machine architecture. On the contrary, you should expect it to ignore the existence of different machine architectures. And likewise when it gets around to describing the class file format, it simply provides an abstract description. It's up to the implementers to write something which runs in a particular machine architecture and which faithfuylly implements the JVM specification.