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I'm just getting started in Android development, and use Netbeans with NBAndroid and SDK 17.

I'd like to use the same Java source code in my Java and Android app.

http://developer.android.com/guide/developing/projects/projects-eclipse.html says how to do it in Eclipse (although it is sketchy on the .JAR connection thing), but I can't seem to make it work in NB.

Based on that link, My understanding is that the correct setup for the Android app is an Android Application project which references an Android Library project which in turn references a .JAR library produced by a Java Library project. I could then also have a Java Application project referring to the same Java Library project.

So, I've set up this project structure... I have an AndroidApp project which is a basic HelloAndroid Activity in a com.ex package. This project includes an AndroidLib library project in the Libraries folder. I also have a LibClass.java file which defines a simple LibClass class which has one function getText() that just returns a String to be displayed. The MainActivity in the AndroidApp calls this to get the String to output.

When I put LibClass.java directly into the AndroidLib project, everything is fine.

But what I want to do is to share the source code with Java.

So I want to move the LibClass.java into the JavaLib library, whose .JAR file is included in the AndroidLib project. However, when I tried that, I get an error in the MainActivity class, complaining it can't find LibClass. Looking at the Projects window, I can see LibClass.class inside the com.ex package in the JavaLib.jar in the Libraries folder of the AndroidLib project. And AndroidLib is visible in the Libraries folder of the AndroidApp project, but it doesn't show any packages or other contents there.

So I feel like I'm just one step away from making this work. Do I need to do something with one or other of the AndroidManifest files perhaps? Or do something with the build.xml files? Or am I on the wrong track altogether?

I'd be really grateful if someone could post a how-to for this.

user998303
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3 Answers3

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I'm trying something similar; I've got Java EE projects, built using Eclipse, and I'm trying to utilize some of that code from my Android projects. This should give me a shared codebase rather than a bunch of confusing SVN externals which I've had to endure before.

Rather than creating JAR files I've found that working with the source and building for the platform works best (well, it has been working but I've got a problem with it at the moment). So, what I'm doing is:

c:\MySvnFolderStructure\MyJavaProjectFolder\src\     (and then all the source under that)
c:\MySvnFolderStructure\MyJavaProjectFolder\android\ (and all the Eclipse Android project gubbins)
c:\MySvnFolderStructure\MyJavaProjectFolder\jee\     (and all the Eclipse JEE project gubbins)

The Android and Java EE projects do not have their own src folders, they both link to the src folder in their parent folder. What this means is that each of the Java implementations is building its own byte code version from the source, and using its own external libraries (like the Apache HTTP ones, for example).

Naturally they can't share stuff like awt (as mentioned in another post), but there's plenty of stuff that does cross-over especially if it's core Java classes that are being used.

Also, it's proving a bit tricky writing JUnit tests as there needs to be some duplication of the test code at the moment because the Android ones need extra instrumentation, but I'm working on it.

Also, see this post about relative paths in Eclipse, which means the folders can be checked-out to different places on different machines (like we all do with our version control check-outs) and still be shared.

Community
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ants_pants
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  • Yes, that's what I wanted to do. I misunderstood the way that Java links/loads JARs. For no particular reason, I had the idea that Java linked/loaded like C. Unresolved references wouldn't prevent execution, so long as they weren't ever dereferenced. So I could import awt.*, but so long as I didn't use awt.* Objects in the Android version all would be fine. This assumption turns out to be very wrong. Thanks for your useful answer. – user998303 May 07 '12 at 02:01
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if I understand your situation correct, you are trying to use a custom java library for both your android and java applications.

For this scenario, you can build the java library first. Instead of adding the java library jar as android library, you can drop the jar directly inside the libs folder of android project and add it to android project's build path.

If you are using ANT scripts for building the java library jar , you can consider adding the source files also as part of jar. This will help you get code assistance when you develop the android part. But this part is purely optional.

MSD
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  • I don't know anything about ANT scripts, but understand they're somewhere in behind Netbeans. If I put the JAR library directly into the Android project, it compiles OK, but won't run. I suspect this is because the JAR in some way depends on the JDK platform rather than the Android platform. There seems to be no way to add the Android platform to a project, except by creating it as an Android project. – user998303 Apr 15 '12 at 21:25
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The problem is that the Java platform in Android is different from the JDK platform.

In particular, the .JAR library CANNOT refer to anything that is not icluded in the Android platform. An example of things you can't refer to is java.awt.* (except you can have java.awt.fonts).

There is also a difference between JDK String and Android String -- Android does not implement the isEmpty() method.

user998303
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  • This string "problem" hapens because you are targeting an old version of android, the method `isEmpty()` was introduced in Android Api 9, Gingerbread, and on JDK 6. When targeting those old versions think you're using jdk 5. – brunodles Apr 05 '15 at 01:47