http://developer.android.com/reference/android/content/Intent.html
Intent Resolution
There are two primary forms of intents you will use.
Explicit Intents have specified a component (via setComponent(ComponentName) or setClass(Context, Class)), which provides the exact class to be run. Often these will not include any other information, simply being a way for an application to launch various internal activities it has as the user interacts with the application.
Implicit Intents have not specified a component; instead, they must include enough information for the system to determine which of the available components is best to run for that intent.
When using implicit intents, given such an arbitrary intent we need to know what to do with it. This is handled by the process of Intent resolution, which maps an Intent to an Activity, BroadcastReceiver, or Service (or sometimes two or more activities/receivers) that can handle it.
May be its saying to mention the component explicitly.