Ill-advised or mistaken usage of a core class (java.* or javax.*) when not building a core library - dalvik

Question

When I clean my project I get the following error:
[2011-10-05 13:47:53 - The Basics] Dx
trouble processing "java/nio/CharBuffer.class":
Ill-advised or mistaken usage of a core class (java.* or javax.*)
when not building a core library.
This is often due to inadvertently including a core library file
in your application's project, when using an IDE (such as
Eclipse). If you are sure you're not intentionally defining a
core class, then this is the most likely explanation of what's
going on.
However, you might actually be trying to define a class in a core
namespace, the source of which you may have taken, for example,
from a non-Android virtual machine project. This will most
assuredly not work. At a minimum, it jeopardizes the
compatibility of your app with future versions of the platform.
It is also often of questionable legality.
If you really intend to build a core library -- which is only
appropriate as part of creating a full virtual machine
distribution, as opposed to compiling an application -- then use
the "--core-library" option to suppress this error message.
If you go ahead and use "--core-library" but are in fact
building an application, then be forewarned that your application
will still fail to build or run, at some point. Please be
prepared for angry customers who find, for example, that your
application ceases to function once they upgrade their operating
system. You will be to blame for this problem.
If you are legitimately using some code that happens to be in a
core package, then the easiest safe alternative you have is to
repackage that code. That is, move the classes in question into
your own package namespace. This means that they will never be in
conflict with core system classes. JarJar is a tool that may help
you in this endeavor. If you find that you cannot do this, then
that is an indication that the path you are on will ultimately
lead to pain, suffering, grief, and lamentation.
[2011-10-05 13:47:53 - The Basics] Dx 1 error; aborting
[2011-10-05 13:47:53 - The Basics] Conversion to Dalvik format failed with error 1

Answer 1

I had this problem. I use Maven to build my android projects. My problem was caused by one of my dependencies depending on the android jars. I updated my pom to exclude android from that dependency and that solved it for me.
<dependency>
<groupId>org.reassembler</groupId>
<artifactId>synth-android</artifactId>
<version>2.5.8</version>
<exclusions>
<exclusion>
<artifactId>junit</artifactId>
<groupId>junit</groupId>
</exclusion>
<exclusion>
<artifactId>android</artifactId>
<groupId>android</groupId>
</exclusion>
</exclusions>
</dependency>
Hope this helps someone, it took me a while to figure out what was going on.

Answer 2

For the benefit of anyone who may have stumbled upon this, this problem can be caused by inclusion of an older library such as android.jar. Removing the .jar file from your buildpath will allow you to compile. Otherwise, you can use the "jarjar" mentioned in the error message to move the .jar file to another package.

Answer 3

Your IDE is misconfigured. Make sure that your scripts or IDE isn't passing rt.jar or android.jar to dx.

Answer 4

In Android Studio, I had included java and javax jar files in my lib folder and there were dependencies related to them (in build.gradle at the app level). I commented them out.
//compile files('libs/ K java-rt-jar-stubs-1.5.0.jar')
//compile 'javax.annotation:jsr250-api:1.0'
//compile files('libs/javax. annotation.jar')
Then i went to the Project View and deleted the jar files. There were some legacy instances of java.awt.geom which I had to purge, but rebuilt project and then i was fine.