java 1.8 versus java 1.7 Compatibility Issue

Question

I am using Java 1.7 in my code, now i want to replace JAVA 1.7 to JAVA 1.8.Is Java 1.8 compatible to Java 1.7. ? Will it work as it before. i mean, all new features of Java 1.8 can be used in the existing piece of code?

• David: Java 8 isn't officially released yet, so you could argue no one can know 100% for sure yet.
• M. Deinum: No. If you use JDK1.8 specific features those aren't going to work on a 1.7 JRE/JDK. If you don't use any specific Java8 features and compile to 1.7 it should still will work.
• Kayaman: @JqueryLearner Really? Do you have a source for that?
• Marko Topolnik: @Kayaman Thread#stop will be removed---not its declaration, but its implementation. I don't know of any other examples, though.
• Marko Topolnik: @StephenC Only the Thread#stop(Throwable) overload has been removed. Reference: cs.oswego.edu/pipermail/concurrency-interest/2013-July/…

Answer 1

The existing piece of code will (ipso facto) not be using any new features of Java 8. If you have a piece of code which works¹ on Java version v, it will also work on all other versions v'> v. That is the long-standing promise of the Java platform.

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¹ By "works" I mean "works as specified, using non-deprecated official JDK APIs".

• Pyranja: As long as your code only depends on public APIs and the Java platform specification, e.g. playing with Unsafe or relying on implementation details like string interning is not covered by that promise.
• carbocation: Not all software is this way. For a prominent example, the GATK which is a genome-analysis toolkit developed by the Broad Institute. It is only compatible with java 1.7, and will throw exceptions if the Java version is 1.8.
• Marko Topolnik: @carbocation The reason may well be that it uses deprecated and/or proprietary APIs which are not part of the JavaSE public API.

Answer 2

It depends.

Your question is a little unclear. "Will it work as before" and "All new features of Java 8 can be used in the existing piece of code" seem mutually exclusive.

If you are using a Lambda Expression (Java 8 feature) you will not be able to compile using JDK7. Conversely if you are compiling using JDK7 you will not be able to use any of the new features in JDK8.

TL;DR: If you have to ask, it probably won't.