Exceptional Puzzlers - Java Puzzlers: Traps, Pitfalls, and Corner Cases - page 97

interface Type1 {
void f() throws CloneNotSupportedException;
}
interface Type2 {
void f() throws InterruptedException;
}
interface Type3 extends Type1, Type2 {
}
public class Arcane3 implements Type3 {
public void f() {
System.out.println("Hello world");
}
public static void main(String[] args) {
Type3 t3 = new Arcane3();
t3.f();
}
}
Solution 37: Exceptionally Arcane
The first program, Arcane1 , illustrates a basic principle of checked exceptions. It may look as
though it should compile: The try clause does I/O, and the catch clause catches IOException . But
the program does not compile because the println method isn't declared to throw any checked
exceptions, and IOException is a checked exception. The language specification says that it is a
compile-time error for a catch clause to catch a checked exception type E if the corresponding
TRy clause can't throw an exception of some subtype of E [JLS 11.2.3].
By the same token, the second program, Arcane2 , may look as though it shouldn't compile, but it
does. It compiles because its sole catch clause checks for Exception . Although the JLS is not
terribly clear on this point, catch clauses that catch Exception or Throwable are legal regardless
of the contents of the corresponding try clause . Although Arcane2 is a legal program, the
contents of its catch clause will never be executed; the program prints nothing.