Transcript Style Rules I

Style Rules I
Style is important
• Everyone agrees that good style is important
– Everyone agrees on most of the essentials
– But some people have “religious wars” over style
– It’s the subtle points that get people really upset
• Subtle points mostly aren’t very important
• The essential points make a clear difference, so these are the ones
people can agree on
• ...Just like a lot of other things in life!
About the book
• This book is a team effort by
many good programmers, not just
one person’s opinions
• The rules have been widely
distributed and commented upon
• The rules reflect widespread and
accepted practices
• And no, I don’t agree with
everything in the book!
Rule 1
Adhere to the style of the original
• Consistent style is very important
• Most times, you will enter an ongoing project, with
established style rules
– Follow them even if you don’t like them
– Don’t try to establish “better” style rules
• It won’t work anyway
• There may be reasons you don’t know about
• If a project has mixed styles with no consistency,
you might try to get people to agree on one
Rule 3
Do it right the first time
• You’re working on a large project, so you use
good style...
• ...but you need a tool to help you do one little job,
so you slap it together quickly
• Guess which program will be around longer and
used by more people?
The “broken window” theory
In inner cities, some buildings are beautiful and
clean, while others are rotting hulks. Why?
Researchers in the field of crime and urban decay
discovered a fascinating trigger mechanism, one
that very quickly turns a clean, intact, inhabited
building into a smashed and abandoned derelict .
A broken window.
From “The Pragmatic
Programmer”
Don't leave “broken windows” (bad designs, wrong
decisions, or poor code) unrepaired. Fix each one as
soon as it is discovered. If there is insufficient time
to fix it properly, then board it up. Perhaps you can
comment out the offending code, or display a "Not
Implemented" message, or substitute dummy data
instead. Take some action to prevent further damage
and to show that you're on top of the situation.
Rule 5
Indent nested code
• Always indent statements that are nested
inside (under the control of) another statement
• if (itemCost <= bankBalance) {
writeCheck(itemCost);
bankBalance = bankBalance - itemCost;
}
• while (seconds > 0) {
System.out.print(seconds + "...");
seconds = seconds - 1;
}
Indenting particular statements
• Java has several kinds of statements, and the book
tells how to indent each
• The general form is usually like this:
– controlling-statement {
nested-statements
}
• Sometimes I violate good style on these slides
because I have to make it all fit!
How much should you indent?
• If you indent too little, the indentation is harder to
see and doesn’t help very much
• If you indent too much, deeply nested code gets
pushed too far to the right
• In general, 2 to 4 spaces seems about right
– The book suggests 2 spaces
– BlueJ’s default is 4 spaces
• Just pick a number and stay with it
Rule 6
Break up long lines
• Scrolling a window horizontally is a pain!
• When you print on standard paper, long lines are
either cut off or wrap in bad places
• I have long used a 72 character limit
• Some editors will show you a limit line
• The book provides good advice on how to break
up long lines (read it!)
Rule 8
Don’t use “hard” tabs
• Once upon a time, you could depend on tab stops
every eight character positions
• Today, every editor has its own idea of where and
how to set tab stops
• If you change editors, your nice indentation gets
ruined
– It’s worse if you use both tabs and spaces
– I have learned this one the hard way!
“Soft” tabs
• Some editors (the good ones) will let you set a
preference so that, when you type a tab, the editor
automatically uses the right number of spaces
instead
– This is what is called a “soft” tab
• BlueJ uses exclusively soft tabs (as of 1.1.4)
– Use tabs all you like in BlueJ
– Remember that most editors don’t do this automatically
What about the rules I skipped?
• Those rules are important, too
• I’m skipping around for a variety of reasons:
– Rules 2 and 4 will make more sense later
– Rule 7 has too much detail to talk about right now (but
it’s a good rule!)
• I’ll try to talk about every rule in class
• This is a good book, worth reading several times
The End