Will programs written against "Java 8" JDK be compatible with "Java 7" JREs?

Question

My question is if Java JDK and JREs have to be compatible to run?

I mean: will Java applications written using JDK version 8 in future work with current JRE's?

Answer 1

The short answer is No.

If you develop your application in JDK 8 and run it with JRE 7, you would get an UnsupportedClassVersionError.