Multi-catch & catch order

Catching related exceptions cleanly

Multi-catch (Java 7+) lets one catch block handle several unrelated exception types separated by |:

try {
    process();
} catch (IOException | SQLException e) {
    // e is effectively final here
    log(e.getMessage());
}

Rules for multi-catch: - The alternatives cannot be in a subclass relationship — catch (Exception | IOException e) is a compile error because IOException is already an Exception. - The variable e is effectively final inside the block — you cannot reassign it.

Catch order matters when you have multiple catch blocks: the most specific (narrowest) exception type must come before the more general ones. The compiler enforces this for checked exceptions but it is equally important for unchecked ones:

try {
    parse();
} catch (NumberFormatException e) {    // more specific first
    System.out.println("bad number");
} catch (IllegalArgumentException e) { // more general second
    System.out.println("bad arg");
} catch (RuntimeException e) {         // most general last
    System.out.println("runtime error");
}

If you put RuntimeException first, the NumberFormatException and IllegalArgumentException blocks become unreachable — a compile error for checked exceptions, but only a warning (not an error) for unchecked ones. The exam tests whether you catch subtypes before supertypes.