9 Mar 2007 (updated 9 Mar 2007 at 05:31 UTC)
»
"Hello, World Considered Harmful" Considered
Harmful
Ralph Westfall's "Hello,
World Considered Harmful" (CACM, 2001) begins by making
a sensible point: the classic K&R example program
"Hello, world" is not a very useful example for an
introductory object-oriented programming course in Java:
public class HelloWorld
{
public static void main(String[] args)
{
System.out.println("hello, world");
}
}
Fair enough: "Hello, world" is fundamentally procedural, and
doesn't teach students anything about how object-oriented
programming (it might also teach them that Java is a
bondage-and-discipline language that forces them to endure
plenty of unnecessarily verbose syntax, but they are going
to learn that eventually regardless).
Unfortunately, Westfall's solution to the problem falls
short of the mark:
class HelloWorld
{
public static void printHello()
{
System.out.println("hello, world");
}
}
public class UseHello
{
public static void main(String[] args)
{
HelloWorld myHello = new HelloWorld();
myHello.printHello();
}
}
Now, we can raise a few minor objections: for
example, it is
pointless to create an instance of a class that contains
only static methods, and it is bad style to invoke a static
method on an instance, IMHO.
But the
essential point is that Westfall's solution merely applies
some irrelevant syntactic sugar. The reason that "hello,
world" isn't a good example of object-oriented programming
is because it isn't object-oriented in the first place. The
intuitive appeal of object-oriented programming stems from
the fact that it is similar to objects in the "real world",
which combine data and behavior. An instance of the
HelloWorld object has neither data nor behavior. In
fact, the modified example serves mostly to showcase an
annoying property of Java: the dependence on static methods
as a way of emulating global functions.
So why
not apply a little creativity, and use a fresh
example that actually illustrates the intuitive appeal
of objects? Model
a few real-world objects as classes, and give them some
behavior: for example, simple geometric shapes like Triangle
and Circle, which can then eventually be developed into a
lesson on inheritance.
(Another improvement would
be to use a better teaching language than Java, but that's
another story.)
