Activity It is a component for displaying the screen of the application, and also has a mechanism for saving / restoring the state and a function for calling other components. Life cycle will be added in the future Fragment Although Fragment is operated on Activity, it has an independent function, so Fragment itself can equip and use View, but Activity controls the basis of the life cycle as a UI screen. The base of the picture-story show is Activity, and each page of the picture-story show is Fragment. Life cycle will be added in the future Context -Interface for passing application environment information globally (entire area of Android OS) -You can respond from other apps such as launching activities, broadcasting, and receiving intents, and you can also access Android-specific resource classes. It has the state of the entire app and is used to pass information such as what it was launched from, what state it is trying to access, and so on. Maybe that's okay. (Excerpt from the following site) http://individualmemo.blog104.fc2.com/blog-entry-41.html Intent Communicate the requirements of each component to the system and connect with the other component as intended. Listener An object that receives an "event occurrence" notification when an "event" occurs