Cross-compiler vs JVM

Question

I am wondering about the purpose of JVM. If JVM was created to allow platform independent executable code, then can\'t a cross-compiler which is capable of producing platfor

Answer 1

The advantage of the bytecode format and the JVM is the ability to optimize code at runtime, based on profiling data acquired during the actual run. In other words, not having statically compiled native code is a win.

A specifically interesting example of the advantages of runtime compilation are monomorphic call sites: for each place in code where an instance method is being called, the runtime keeps track exactly what object types the method is called on. In very many cases it will turn out that there is only one object type involved and the JVM will then compile that call is if it was a static method (no vtables involved). This will further allow it to inline the call and then do even more optimizations such as escape analysis, register allocation, constant folding, and much more.

In fact, your criticism could (some say, should) be turned upside-down: why does Java define bytecode at all, fixing many design decisions which could have been left up to the implementation? The modern trend is to distribute source code and have the JIT compiler work on that.