Android：PendingIntent是Intent的一种形式，那么PendingIntent为什么不是Intent的子类呢？

Question

They say that

Generally, when there exists an "is-a" relationship between two entities, there is an inheritance relationship in terms of OOP.

For example

"A mountain bike is a bicycle."

So MountainBike is a subclass of Bicycle as well, as a MountainBike inherits the properties of Bicycle , and has some of its own as well.

Now, generally speaking a PendingIntent is an Intent, isn't it? So why is a PendingIntent a subclass of Intent?

Reference: Developer docs

Answer 1

generally speaking a PendingIntent is an Intent, isn't it?

A PendingIntent can be best thought of as a wrapper around an Intent , identifying an operation to be performed (start an activity, start a service, send a broadcast) and a security context under which that operation should be performed.

Hence, a "has-a" relationship model is a perfectly reasonable approach here.