If your Android app crashes, then because of an uncaught RuntimeException like a NullPointerException.
In this video we will learn, how to read the Logcat stack trace to find out what exception caused our app to crash and where it happened in our code, so we can provide more specific information when we ask for help.

Java RuntimeException documentation:
docs.oracle.com/javase/7/docs/api/java/lang/RuntimeException.html