CODEWITHSUNDEEP
javamacroscompatibility
jacobq
jacobq

Reputation: 11577

Does Java have something like "shims" in JavaScript, preprocessing in C, or "macros" in general?

In the JavaScript world it often happens that a user's browser does not implement a feature but it can be supported by adding some additional code as a work-around. This is often called a "shim" (or "shiv"). In C I have done something similar at compile-time using preprocessing like #define ENABLE_XYZ_SUPPORT 1 and then #if ENABLE_XYZ_SUPPORT 1.

Is there something like this in Java? Namely, I would like to be able to compile some source code designed for Java 1.7 with Java 1.6. Perhaps there is a library for this if there is no built-in language construct?

Background: I am somewhat new to Java and am developing my first significantly large project (basically a servlet that conditionally assembles data from various sources). Since this is a brand new project it seemed reasonable to take advantage of some of the new features of Java 1.7 such as implementing the AutoCloseable interface for objects rather than just Closeable so that they could be used with try-with-resources. However, it would be nice if this application could be built to run on Java 1.6 as well in case it needed to. If I could add a parameter or something to enable defining my own AutoCloseable interface then this could compile since I am not actually using try-with-resources -- just trying to use the most appropriate interfaces.

I realize that I could do something like have maven run an external tool to replace AutoCloseable with Closeable if it were building for 1.6. However, that's not really what I'm looking for (not general enough).

Update: To clarify, I'm wondering if I can do something conditionally at compile-time like this:

#if java version < 1.7

    public interface AutoCloseable {
        void close() throws Exception;
    }

#endif

BTW, I am using maven with this project, so if it has a feature that would help here that might be worth considering.

Upvotes: 0

Views: 1766

Answers (3)

Michael Krussel
Michael Krussel

Reputation: 2656

If you're close methods only throw IOExceptions, you can implement Closeable. This interface was introduced in Java 1.5. In Java 7, it was modified to extend AutoCloseable. Your library should then support try with resources for clients that are using Java 7, but still be compatible with Java 6.

I've not tried this, but it seems like it should work.

Upvotes: 2

Michael Berry
Michael Berry

Reputation: 72359

Since this is a brand new project it seemed reasonable to take advantage of some of the new features of Java 1.7 such as implementing the AutoCloseable interface for objects rather than just Closeable so that they could be used with try-with-resources. However, it would be nice if this application could be built to run on Java 1.6 as well in case it needed to.

This is a no go with Java - it's backwards compatible, but not forwards compatible. If you try and hack your way around getting various Java 7 language features in Java 6 (of which AutoCloseable is one) you'll end up with a horrific mess of a project that would cause many more problems than it solved.

Java 7 support is relatively widespread now - it wasn't for a while but that situation has now changed, so I don't think it's unreasonable to require anyone building or running the application to have Java 7 installed. If this is something you have to have, then I'm afraid the only sensible option is to forfeit the Java 7 language features and target 1.6 directly.

Upvotes: 2

namero999
namero999

Reputation: 3012

You can't run java code that makes uses of the new construct of java 7 (such as try-with-resources) on java 6 JVMs, so there's no compiler or code trick that will help you on that, unfortunately. You should have two codebases if you want to support and old version.

Upvotes: 2

Related Questions