The basic idea behind exception handling is that client code does not clutter the main logic flow with checks for error codes, but specifies instead an *exception handler* to “catch” exceptions. When something goes wrong, instead of returning an error code, the method that detects the exceptional situation interrupts the main flow of execution by *signaling* an exception. This does two things: it captures essential information about the context in which the exception occurred, and transfers control to the exception handler, written by the client, which decides what to do about it. The “essential information about the context” is saved in an `Exception` object; various classes of `Exception` are specified to cover the varied exceptional situations that may arise. pdf 
(via Juan Mnaul's Academia account)