What is the difference between @UiThread and @MainThread annotation in Android?

@MainThread is the first thread that starts running when you start your application

@UiThread starts from Main Thread for Rendering user Interface

Also from Android Documentation

Note: The @MainThread and the @UiThread annotations are interchangeable so methods calls from either thread type are allowed for these annotations.

https://developer.android.com/tools/debugging/annotations.html#thread-annotations

More complete explanation: It's possible for a UI thread to be different from the main thread in the case of system apps with multiple views on different threads. Therefore, you should annotate methods associated with an app's view hierarchy with @UiThread and annotate only methods associated with an app's lifecycle with @MainThread.