注：在《疯狂android讲义》中，此属性称为Component，官方文档中称为ComponentName。
1、The name of the component that should handle the intent. This field is a ComponentName object — a combination of the fully qualified class name of the target component (for example "com.example.project.app.FreneticActivity") and the package name set in
the manifest file of the application where the component resides (for example, "com.example.project"). The package part of the component name and the package name set in the manifest do not necessarily have to match.
The component name is optional. If it is set, the Intent object is delivered to an instance of the designated class. If it is not set, Android uses other information in the Intent object to locate a suitable target
— see Intent Resolution, later in this document.
The component name is set by setComponent(), setClass(), or setClassName() and read by getComponent().
2、ComponentName用于显式指定Intent所对应的组件。