A co-worker and I recently had a discussion about Java versions and the JVM. I use Java 7 but we use Java 6 for our client (while he says that some are still on 5). My immediate thought was, why can't we target those VMs too?
The Java VM is somewhat different than a real machine in that it has a bunch of runtime features. Type checking, exception handling, garbage collection, etc. But it's still a virtual machine which has a bytecode. (Which is why we can have things like C to JVM compilers.) So why can't we target older VMs with newer version of Java? Why does the language and the runtime have to be tied together? Besides the obvious performance penalties, it seems like it should be completely possible to compile Java 7 code to the Java 6 JVM. (And considering how little changed from Java 6 to 7, I can't imagine the compiler changes being that extensive.)