It is "mostly" backwards compatible. Applets and everything related to them where dropped. A few interface dependencies where changed to improve modularity of t

It is "mostly" backwards compatible. Applets and everything related to them where dropped. A few interface dependencies where changed to improve modularity of the runtime. Widely used hacks like sun.misc.unsafe are getting replaced with official APIs and locked down. Development of some Java EE packages has been taken over by a third party, so they are no longer packaged within the java namespace. To name just a few of the bigger examples.