Android apps have three core components: activities, services, broadcast receivers. They are all activated by a message called intents. Intent messages are a mechanism for delaying runtime binding between components in the same or different applications. Intent is a passive data structure that holds an abstract description of the operation to be performed, or, in the case of broadcasting, usually something has already occurred and is being declared.
Intent is divided into explicit inten and implicit intent.
Explicit Intent: Specifies the target component by name. Typically used for intra-application messaging, such as an activity that initiates a dependent service or initiates a sister activity.
Implicit intent: Does not specify the name of the target, which is typically used to activate components in other applications.
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Android Intent Object