Can call java 7 compile java code from java 6 compiled code

Question

I have program compiled on java 6. And library compiled on java 7. Can I call from java 6 compiled code to java 7 compiled code or I will have run time errors. I know that I will have errors on compilation, but i will change jar after compilation. I run my application on jvm 7.

Answer 1

In general Java 7 is backward compatible, so you can use libraries compiled with Java 6.

For example: If your library compiled with Java 6 uses a javax package, it will use the library comming with Java 7 and compiled with Java 7.

I use Apache CXF 2.4.6 (compiled with Java 5) with Java 7. Apache CXF calls Servlet API (compiled with Java 6) of JBoss 7.

Answer 2

Yes, you can, but there are issues with the classfile formats; see this question for the exact mapping of Java versions and classfile format versions.

Specifically, if you have source code A that you are compiling with JDK 6 but you have JAR in the compilation path that has .class files that are with major version 51, then the compilation will fail because the compiler will not be able to load the class files.

However, when compiling you can specify a '-target 1.6' flag so that the generated classfile is compatible with Java 6. If you have access to the source of your library you can recompile it with that target so that it's compatible with a 1.6 compiler.

Lastly (and obviously), the classfile format version must be understood by the JVM.