However, as of ADT 14, in a library project, they will be declared like this:

public static int main=0x7f030004;

 

In other words, the constants are not final in a library project. The reason for this is simple: When multiple library projects are combined, the actual values of the fields (which must be unique) could collide. Before ADT 14, all fields were final, so as a result, all libraries had to have all their resources and associated Java code recompiled along with the main project whenever they were used. This was bad for performance, since it made builds very slow. It also prevented distributing library projects that didn't include the source code, limiting the usage scope of library projects.

 

The reason the fields are no longer final is that it means that the library jars can be compiled once and reused directly in other projects. As well as allowing distributing binary version of library projects (coming in r15), this makes for much faster builds.

However, it has one impact on the source code of the library. Code of the following form will no longer compile:

 

 

 

That's because the switch statement requires all the case labels, such as R.id.button1, to be constant at compile time (such that the values can be directly copied into the .class files).

 

The solution for this is simple: Convert the switch statement into an if-else statement. Fortunately, this is very easy in Eclipse. Just place the caret on the switch keyword, and press Ctrl-1 (or Cmd-1 on Mac):

In the above scenario, it will turn the switch statement into this:

 

 

This is typically in UI code and the performance impact is negligible.

 

We have a detector which finds these errors (non-constant case labels referencing an R field) and provides a brief explanation of the problem (and points to this page for more information.)

More information about the automatic detection.