Mixing Java 1.4 and 1.6 bytecode in a class hierarchy

Question

The question first, the story will follow:

Is it safe to mix different bytecode version in a class hierarchy? What are the risks?

For a case, Class C extends

Answer 1

These links seem relevant. They document the few edge cases that could break compatibility between 1.4 and 1.5 and between 1.5 and 1.6.

The biggest differences that could cause problems that I can think of is that enum became a keyword, but that would only effect a 1.5+ JVMs when loading an older class file (which doesn't seem to be what you will be doing). The other thing is annotations. The above links seem to suggest everything would be fine, but I would be wary about what would happen if an older JVM loaded up a class with runtime annotations.

Other than that I don't think there have been any bytecode changes between the first version of java and java 6. Meaning the only problems you should encounter are changes to functionality the API or deprecations (listed in the links above).