Managing Complexity Programming is more than just syntax Learning things that matter Things change rapidly in computer science CIT591 is primarily an introductory programming course Languages go in and out of popularity operating systems change even programming styles changes Half of what you learn in my class will be outdated in five years It uses this year s popular programming language Unfortunately that language is so complex that learning the syntax takes time away from learning to program In this slide set I m talking about things that will not be outdated in five years But my examples will be from Java Programs should work Programs should work correctly Many programs must be highly reliable The need for correctness isn t going to change any time soon Programs should continue to work correctly after they are modified or updated or had new features added Medical programs space vehicle control programs sales programs income tax programs Household robots self driving automobiles Thus it is important to be able to modify programs safely This means Clear concise readable programs Good tests especially regression tests Readability Can we read a program or do we have to decipher it Here s a method I would consider readable public boolean isLeapYear int year if year 400 0 return true if year 100 0 return false return year 4 0 At this point you may feel that all programs have to be deciphered I feel the same way when I try to read German With practice deciphering changes to reading mostly Another readable method void playGame boolean playAgain true while playAgain int computersScore 0 int usersScore 0 boolean nobodyHasWonYet true while nobodyHasWonYet computersScore computersScore resultOfComputersTurn usersScore usersScore resultOfUsersTurn printCurrentScores computersScore usersScore nobodyHasWonYet computersScore WINNING SCORE usersScore WINNING SCORE printFinalScores computersScore usersScore playAgain askUser Do you want to play again A less readable method private static int giveRandomNumber int minValue int maxValue if minValue maxValue int temp maxValue maxValue minValue minValue temp Random random new Random int temp if maxValue 0 minValue 0 temp 0 random nextInt minValue 1 while maxValue temp temp 0 random nextInt minValue 1 w else temp random nextInt maxValue 1 while minValue temp temp random nextInt maxValue 1 w e return temp What makes a method readable Short enough to see the entire method at once without scrolling Does a single thing Has a meaningful descriptive name Is properly formatted and follows established conventions Has comments that further clarify what the method does Calls methods with meaningful descriptive names Uses established idioms Very idiomatic for int i 0 i array length i Less idiomatic for row 0 row array length 1 row Has a short memorable parameter list with well chosen parameter names Doesn t do weird things Doesn t change parameter objects unnecessarily If available outside the class works for any valid object That is it doesn t depend on some other method being called first What makes a program modifiable Good tests are essential More bugs are introduced when correcting a program than at any other time Frequently in order to introduce new features you have to refactor reorganize a program If you have a complete set of tests you can do this much more safely If you have a complete set of tests you can do this much more safely You can add features but you cannot change features that other people that is other parts of the project depend upon At least not without an extremely convincing reason You can t change what methods do but you can change how they do it You can only change how methods work if nothing else depends on it This is why you must hide as much as possible of your implementation Example A modifiable program public class Lexicon private String words private int counts private int numberOfWords 0 etc An unmodifiable program public class Lexicon String words int counts int numberOfWords 0 etc Information hiding When you provide a class to a project You should provide everything that is needed by the project You should not provide anything that isn t needed If you do someone somewhere will take advantage of it If you then change it you will get the blame There is a lot more to be said on the topic of information hiding but I don t have the time right now to say it all I will add this much Information hiding also applies to your JUnit tests If you don t want your tests to break when you make correct changes to your program don t depend on features that should be hidden The End
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