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

The JVM byte code is not siginificantly different between Java 1.0 and Java 6. In Java 7 they add one new instruction. Woohoo.

There are so little changes in how the byte code works that

• The JVM doesn't support nested classes accessing private members of outer classes, this works through generated code.
• The JVM doesn't support runtime checks for generics e.g you cannot new T() where T is a generic.

Basically, they make the JVM smarter and faster but until recently changing the model of how the byte code works has been avoided at all costs.