Transcript media:cc2e-chapter07.pptx

Chapter 7: High Quality
Routines
By Raj Ramsaroop
What Is A Good Routine?
 A routine is a:




Function (C++).
Method (Java).
Procedure (Visual Basic).
Macro.
 A routine should have a single purpose.
Example: A Bad Routine
Why Was That A Bad Routine?







Name: HandleStuff().
Too many parameters.
No logical ordering to parameters.
Looks like it’s trying to do more than one task.
Not logically laid out.
Input variable is changed.
Unused parameters.
Why/When Create A Routine?




Biggest reason: reduce complexity.
Minimize code, avoid duplicate code.
Make your code more maintainable.
Easier to read.
Why/When Create A Routine? Cont.
 Avoid duplicate code.
 Only need to check one place.
 Avoid writing the same thing twice.
 Similar code in different routines – split them up.
 Hide sequences.
 Keeps code simple.
 E.g. if you get data from a user and data from a file,
neither routine should depend on each other.
Why/When Create A Routine? Cont.
 Improve portability.
 Make your code independent of hardware/software, or the
project you are working on.
 Can be reused – enforces object-oriented concepts.
 Simplify complicated boolean tests.




E.g. isVisible()
Details of the test are out of the way.
The name is descriptive.
Emphasizes it’s significance.
Can Code Sometimes Be Too Small
For A Routine?
 Depends:
 If you keep repeating the same line.
 One line of code can balloon into something bigger.
 Makes code more readable.
Routine Cohesion
 Cohesion refers to how closely the operations in the
routine are related.
 Ensures routines perform one task well – and nothing else.
 Acceptable types of cohesion:
 Functional cohesion – the best type, is when a routine
performs only one function.
 Sequential cohesion.
 Communicational cohesion.
 Temporal cohesion.
Unacceptable Types Of Cohesion
 Procedural cohesion – operations that are in a specific
order and are combined for that specific reason.
 Logical cohesion – basically methods with big ‘if
statements’
 Operations are not usually logically related.
 Only time this would be acceptable would be something
like an event handler.
 Coincidental cohesion – if you have this it probably
means you need to redesign your program!
Naming Routines
 Name can be as long as it needs to be – as long as it
doesn’t sound silly!
 Make it descriptive.
 Avoiding meaningless verbs (e.g. processOutput(),
calculateData()).
 Don’t differentiate functions solely by a number!
 Use what the function returns to name the function. E.g.
customerId.next(), printer.isReady()
 To name a procedure, use a strong verb followed by an
object. E.g. printReport(), calculateInvoice()
 Use opposites such as get/set, open/close, first/last etc
How Long Should A Routine Be?
 A line is a noncomment, nonblank line of code.
 Book suggests up to 200 lines.
 They can be as long as they need to be as long as you
focus on cohesion.
Using Routine Parameters
 Put parameters in “input-modify-output” order.
 As opposed to randomly or alphabetically.
 Implies a sequence of operations.
 If several routines take similar parameters, put them in the same
order.
 Use all parameters.
 Status and error variables go last.
 Don’t use routine parameters as working variables.
 Document the input variables (range, units, values that should never
appear etc).
 Limit number of parameters to 7.
 Check parameter types (mismatched types etc).
When To Use A Function Or
Procedure And Return Values
 A function is a routine that returns something.
 A procedure is a routine that does something, but
does not return anything.
 You can combine the two.
 Return values should return an object, not a
reference or pointer to local data.