14.18.1 Execution of try-catch

Our supreme task is the resumption of our onward, normal way.
—Warren G. Harding, Inaugural Address (1921)

A try statement without 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 no further action is taken and the try statement completes normally.
• 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 (§5.2) 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. If that block completes normally, then the try statement completes normally; if that block completes abruptly for any reason, then the try statement completes abruptly for the same reason.
  • If the run-time type of V is not assignable to the parameter of any catch clause of the try statement, then the try statement completes abruptly because of a throw of the value V.
• If execution of the try block completes abruptly for any other reason, then the try statement completes abruptly for the same reason.

In the example:

class BlewIt extends Exception {
	BlewIt() { }
	BlewIt(String s) { super(s); }
}
class Test {
	static void blowUp() throws BlewIt { throw new BlewIt(); }
	public static void main(String[] args) {

		try {
			blowUp();
		} catch (RuntimeException r) {
			System.out.println("RuntimeException:" + r);
		} catch (BlewIt b) {
			System.out.println("BlewIt");
		}
	}

}

the exception BlewIt is thrown by the method blowUp. The try-catch statement in the body of main has two catch clauses. The run-time type of the exception is BlewIt which is not assignable to a variable of type RuntimeException, but is assignable to a variable of type BlewIt, so the output of the example is:

BlewIt