### Ant buildfiles as project builders

Our second practical example of using Ant buildfiles in Eclipse is a 'project builder'. This is an Ant buildfile that has been designated to run whenever a project is built. The uses for such a buildfile are many:

- Generate a .jar file containing class files from your project
- Perform some type of pre or post build processing on source or binary files in your project. For example:
  - Pre-processing source files to instrument them for performance analysis
  - Obfuscating binary files to prevent reverse engineering
- Copy class files to some location (for instance, on a network)

For this example, we will create an Ant buildfile that creates a .jar archive of the class files in a project. Note that this is similar to the example in the last chapter, in which we used an Ant buildfile to generate .jar files for an Eclipse plug-in. This example differs in that it works for any Eclipse project, whether or not it is also an Eclipse plug-in.