I believe older java versions are already incompatible with newer jvms.  I couldn&#x27;t find it explicitly stated but i&#x27;d be surprised if 1.4 code worked 100% correct on a 1.7 jvm.<p>My experience so far is that the list of incompatibilities (<a href="http:&#x2F;&#x2F;www.oracle.com&#x2F;technetwork&#x2F;java&#x2F;javase&#x2F;compatibility-417013.html#jdk7" rel="nofollow">http:&#x2F;&#x2F;www.oracle.com&#x2F;technetwork&#x2F;java&#x2F;javase&#x2F;compatibility-...</a>) between versions makes it nearly impossible to just drop code between versions.  It will run, but often implementation details have changed causing significant bugs.  Your mileage may vary