[Bluej-discuss] Execute BlueJ

[Stephen Bloch]

Frans writes:
>I download the tutorial, and in pag e 8 said that to execute we must
>right click and choose the method.
>
>in my opinion, run the code usually using main args
>
>anyone have a tips for this? why you approaceh using method?
>
>i see the different paradigm to execute java class in bluej, what is the
>best way to explain about this?

As others have pointed out, pedagogical reasons.

One of my principles for teaching beginning programming is to teach 
only those language features that are necessary in order to teach a 
particular programming principle, and to teach them one at a time 
when they're actually needed.

If you start with "public static void main(String[] args) { ... }", 
you have an unattractive choice:
(a) you can try to explain access specifiers, static methods, return 
types and the lack thereof, data types, arrays, and parameter 
declarations, all on the first day of the term, or
(b) you can tell students "Just copy this down and trust me, you'll 
understand it by the end of the semester."
Naturally, everybody chooses (b), but wouldn't it be nice to have 
students writing code that they actually UNDERSTAND?  Wouldn't it be 
nice if the only syntax they needed was actually RELEVANT to the 
problem they were trying to solve?

Another pedagogical benefit is ease of testing.  If your program can 
only be invoked from a "main" method, then every time you want to 
test a new or modified part of the program, you have to modify the 
"main" method to make appropriate calls to that part, and check or 
output the answers.  To avoid some of this re-coding, you'll probably 
write the "main" method to get its testing data from input, which 
means you can't automate your test suites, which means regression 
testing is a hassle and you're unlikely to do it, which means that 
when you make a modification to one part of the program that breaks 
another part, you won't find out about it immediately.  By contrast, 
if you can easily write and invoke testing methods directly, it's 
easier to automate test suites than to type in the testing data every 
time, and regression testing takes one or two mouse clicks so you'll 
probably actually do it.

Yet another is that you can (if you wish) postpone the treatment of 
I/O.  Java has many wonderful features; in particular, its treatment 
of text I/O is powerful, general, and a royal pain to use (even with 
the 1.5 Scanner class).  I/O coding in ANY language tends to be 
fiddly, with a high ratio of "tweak time" to important ideas. 
Furthermore, I/O varies more from language to language than any other 
common language feature, so anything students learn about I/O in this 
language is only a slight benefit in other languages.  BlueJ (and 
DrJava and ProfessorJ) allows you to invoke a method on data 
directly, and see the result directly, without writing any I/O code 
at all.  As the instructor, you can therefore postpone I/O until 
whenever you think it fits naturally into your course.
-- 
							Stephen Bloch
							Math/CS Dept
 
Adelphi University
 
sbloch at adelphi.edu