14.18.2 Execution of try-catch-finally

After the great captains and engineers have accomplish'd their work,
After the noble inventors—after the scientists, the chemist,
the geologist, ethnologist,
Finally shall come the Poet . . .
—Walt Whitman, Passage to India (1870)

A try statement with a finally block is executed by first executing the try block. Then there is a choice:

• If execution of the try block completes normally, then the finally block is executed, and then there is a choice:
  • If the finally block completes normally, then the try statement completes normally.
  • If the finally block completes abruptly for reason S, then the try statement completes abruptly for reason S.
• If execution of the try block completes abruptly because of a throw of a value V, then there is a choice:
  • If the run-time type of V is assignable to the parameter of any catch clause of the try statement, then the first (leftmost) such catch clause is selected. The value V is assigned to the parameter of the selected catch clause, and the Block of that catch clause is executed. Then there is a choice:
    • If the catch block completes normally, then the finally block is executed. Then there is a choice:
      • If the finally block completes normally, then the try statement completes normally.
      • If the finally block completes abruptly for any reason, then the try statement completes abruptly for the same reason.
    • If the catch block completes abruptly for reason R, then the finally block is executed. Then there is a choice:
      • If the finally block completes normally, then the try statement completes abruptly for reason R.
      • If the finally block completes abruptly for reason S, then the try statement completes abruptly for reason S (and reason R is discarded).
  • If the run-time type of V is not assignable to the parameter of any catch clause of the try statement, then the finally block is executed. Then there is a choice:
    • If the finally block completes normally, then the try statement completes abruptly because of a throw of the value V.
    • If the finally block completes abruptly for reason S, then the try statement completes abruptly for reason S (and the throw of value V is discarded and forgotten).
• If execution of the try block completes abruptly for any other reason R, then the finally block is executed. Then there is a choice:
  • If the finally block completes normally, then the try statement completes abruptly for reason R.
  • If the finally block completes abruptly for reason S, then the try statement completes abruptly for reason S (and reason R is discarded).

The example:

class BlewIt extends Exception {
	BlewIt() { }
	BlewIt(String s) { super(s); }
}

class Test {

	static void blowUp() throws BlewIt {

		throw new NullPointerException();

	}

	public static void main(String[] args) {
		try {
			blowUp();
		} catch (BlewIt b) {
			System.out.println("BlewIt");
		} finally {
			System.out.println("Uncaught Exception");
		}
	}

}

produces the output:

Uncaught Exception
java.lang.NullPointerException
	at Test.blowUp(Test.java:7)
	at Test.main(Test.java:11)

The NullPointerException (which is a kind of RuntimeException) that is thrown by method blowUp is not caught by the try statement in main, because a NullPointerException is not assignable to a variable of type BlewIt. This causes the finally clause to execute, after which the thread executing main, which is the only thread of the test program, terminates because of an uncaught exception (§20.21.31), which results in printing the exception name and a simple backtrace.