Watch Out For OpenJDK Differences on Android N

Android N is shipping with its java.* and javax.* classes
derived from the OpenJDK, rather than from Apache Harmony. Many of
the Harmony classes were modified in Android since Android 1.0, and
the JDK itself has gone through a couple of major releases. So,
while there are large test batteries designed to confirm that everything
is compatible, some changes in behavior are likely to slip through
the cracks.

For example, eagle-eyed developers have noted that
java.io.File path normalization has changed
and that
java.text.DecimalFormat has changed.
I have reproduced both of their test results and can confirm the
differences.

It is entirely possible that these will be altered to be compatible with
past versions of Android before Android N ships in final form. It is
theoretically possible that these are the only two such differences, but
that seems unlikely.

Hence, more so than with past developer previews, it is key for you to
be testing your code early and thoroughly, to see whether you trip over
similar sorts of JDK class differences. At minimum, you will have time
to find a workaround. Even better, file an issue, and see if the
incompatibilities can get fixed.