Question

I’ve recently moved to Java 7 in one of my projects. I claim that it can run on Java 1.5 simply because there’s nothing I depend on that is in Java 6 or 7. However when compiling today I noticed this:

bootstrap class path not set in conjunction with -source 1.5

Google has found little information on this warning. Does this mean that you can’t compile to Java 1.5 from Java 1.7?

Answer 1

This Oracle blog explains the warning:

http://blogs.oracle.com/darcy/entry/bootclasspath_older_source

The reason is, that if you fail to set rt.jar for the older platform, then:

If the second step is not taken, javac will dutifully use the old
language rules combined with new libraries, which can result in class
files that do not work on the older platform since references to
non-existent methods can get included.