Is Java bytecode compatible with different versions of Java?

Question

If I compile an application using Java 5 code into bytecode, are the resulting .class files going to be able to run under Java 1.4?

If the latter can wo

Answer 1

No they are not. .class files are forward compatible only.

Java5 framework implies that your library is probably using generics or annotations that are incompatible with your 1.4 environment. You have to evaluate how much risk there is for you to run your 1.4 application under a 1.5 JVM to enable use of the frameworks you require.

In general I've found moving to 1.5 to be mostly painless, but diligent testing is called-for.