Exceptional Puzzlers - Java Puzzlers: Traps, Pitfalls, and Corner Cases - page 103

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Puzzle 39: Hello, Goodbye
This program adds an unusual twist to the usual Hello world program. What does it print?
public class HelloGoodbye {
public static void main(String[] args) {
try {
System.out.println("Hello world");
System.exit(0);
} finally {
System.out.println("Goodbye world");
}
}
}
Solution 39: Hello, Goodbye
The program contains two println statements: one in a try block and the other in the
corresponding finally block. The TRy block executes its println and finishes execution
prematurely by calling System.exit . At this point, you might expect control to transfer to the
finally block. If you tried the program, though, you found that it never can say goodbye: It prints
only Hello world . Doesn't this violate the principle explained in Puzzle 36 ?
It is true that a finally block is executed when a try block completes execution whether normally
or abruptly. In this program, however, the try block does not complete execution at all. The
System.exit method halts the execution of the current thread and all others dead in their
tracks. The presence of a finally clause does not give a thread special permission to continue
executing.
When System.exit is called, the virtual machine performs two cleanup tasks before shutting down.
First, it executes all shutdown hooks that have been registered with Runtime.addShutdownHook .
This is useful to release resources external to the VM. Use shutdown hooks for behavior that
must occur before the VM exits. The following version of the program demonstrates this