0

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?

user2246674
  • 7,621
  • 25
  • 28
luke1985
  • 2,281
  • 1
  • 21
  • 34
  • possible duplicate of [Is JDK "upward" or "backward" compatible?](http://stackoverflow.com/questions/4692626/is-jdk-upward-or-backward-compatible) – Julien Sep 21 '13 at 17:46

3 Answers3

2

It is possible to use cross-compilation options when compiling. Do that and it will be possible to compile code with SDK 8 that is compatible with Java 1.1. It won't be very advanced code for 1.1, but it will run.

Andrew Thompson
  • 168,117
  • 40
  • 217
  • 433
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.

Terry Li
  • 16,870
  • 30
  • 89
  • 134
0

This question is two part:

  1. JDK vs JRE
  2. forward / backward compatibility.

JRE is the acronym for Java Runtime Environment. JDK is the acronym for Java Development Kit: a set of tools which you use to develop Java programs. The JDK also contains a full JRE. In general there is no compatibility issue between the two. But you might want to take care not to use libraries which are only available in the JDK (for example code generation or the tools.jar)

Java itself is compiling to bytecode, which is forward compatible. That means you can use bytecode of any Java version and run it with any newer version. The other way around generally doesn't work and is checked by using the class file version ("java.lang.UnsupportedClassVersionError: Test : Unsupported major.minor version 51.0").

Then there are Java libraries, including the core libraries. So far there was never anything removed from them, so they are forward compatible. This is probably going to change with Java 9 where a very small usually unused library functions are removed.

Regarding to backwards compatibility, this is possible by setting the Java compiler to produce Bytecode of an older version. Up until Java 8, the compiler was always able to produce bytecode of the last two major versions as well. However, you might successfully compile a Java 8 source to Java 6, but not be able to run it. That is the case when you use libraries that are only available on a never Java. For such cases there is for example the maven animalsniffer plugin which will verify that when you compile against an older version, you actually only use libraries existing in said version.

Fabian Lange
  • 1,786
  • 1
  • 14
  • 18