## The plug-in class

So far, we've been looking at the different extensions that are provided by the readme tool. Let's look at the general definition of the readme tool plug-in.

### Plug-in definition

The readme tool plug-in is defined in the MANIFEST.MF file.

    Manifest-Version: 1.0
    Bundle-ManifestVersion: 2
    Bundle-Name: %Plugin.name
    Bundle-SymbolicName: org.eclipse.ui.examples.readmetool; singleton:=true
    Bundle-Version: 3.3.0.qualifier
    Bundle-ClassPath: readmetool.jar
    Bundle-Activator: org.eclipse.ui.examples.readmetool.ReadmePlugin
    Bundle-Vendor: %Plugin.providerName
    Bundle-Localization: plugin
    Require-Bundle: org.eclipse.ui,
     org.eclipse.core.resources,
     org.eclipse.core.runtime,
     org.eclipse.ui.views,
     org.eclipse.ui.ide,
     org.eclipse.jface.text,
     org.eclipse.text,
     org.eclipse.ui.workbench.texteditor,
     org.eclipse.ui.editors
    Eclipse-AutoStart: true
    Eclipse-AutoStart-comment: Use Eclipse-AutoStart instead of Eclipse-LazyStart because the readme example should run against 3.1 as well as 3.2.

The plug-in definition includes the Bundle-Name, Bundle-SymbolicName (plug-in id), Bundle-Version, and Bundle-Vendor of the plug-in. We saw most of these parameters before in our hello world plug-in. The readme tool also defines a specialized plug-in class, ReadmePlugin.

The name of the jar file is also provided. File names specified in Bundle-ClassPath are relative to the plug-in's directory, so the readme tool's jar file should be located directly in the plug-in's directory.

The Require-Bundle element informs the platform of the readme tool's dependencies. The workbench UI plug-ins are listed as required plug-ins, along with the various core, jface, and text plug-ins.

### AbstractUIPlugin

The ReadmePlugin class represents the readme tool plug-in and manages the life cycle of the plug-in. As we saw in the Hello World example, you don't have to specify a plug-in class. The platform will provide one for you. In this case, our plug-in needs to initialize UI related data when it starts up. The platform class AbstractUIPlugin provides a structure for managing UI resources and is extended by ReadmePlugin.

AbstractUIPlugin uses the generic startup and shutdown methods to manage images, dialog settings, and a preference store during the lifetime of the plug-in. We'll look at the specifics of the ReadmePlugin class when we work with dialogs and preferences.