What Is "Compiler Compliance Level" in Eclipse

What is compiler compliance level in Eclipse?

The compiler compliance setting tells the compiler to pretend it's a different version of Java.

The Java 8 compiler will produce class files in the Java 8 version of the class file format, and accept Java 8 source files. JRE 6 can't load this version, because it was created after JRE 6 was.

If you set the compliance level to "JRE 6", it will instead compile Java 6 source files into Java 6 class files.

It's like saving a Word document as "Word 97-2003 format" - so that Word 97-2003 can read your document. You're saving the class files in Java 6 format so that Java 6 can read them.

Is setting eclipse java compiler compliance level 1.6 same as compile using JDK 1.6?

You can actually specify the .class files version compatibility in the "Preferences->Java->Compiler" (project specific), so at worst you are benefitting from a more recent compiler building probably exactly the same bytecode as using JDK 1.6.

"Compliance 1.6" however does not ensure that you get exactly the same result as using JDK1.6, but java standard ensures applications built with 1.6 will run the same on a >= 1.6 JRE.

So if you are really afraid of incompatibilities, build the project (on your CI server I suppose) with a project specific setting 1.6 on a machine with both JRE 1.6 for this one, and 1.7 for other projects, and bundle a 1.7 in your distribution, it is guaranteed to run ok by Sun/oracle/java.

i.e. if the code is built with JDK 1.6, and used by other JDK >= 1.7 code you are fine with respect to versioning. Probably this is the case of many jars you use everyday.

However, building the code that is stamped 1.6, with a real JDK 1.6 is the only sensible thing to do if you are afraid of real world problems (money involved).

So I think then you are safe to "claim support", build in 1.6 and use the jar in 1.7.

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