1	CS110 Lecture 5 Tuesday, February 10, 2004 Announcements hw2 due Thursday when labs close hw1 returned today (answer posted soon) tutoring available (see course web page) Agenda questions new, constructors client classes; javadoc LinearEquation and Temperatures classes testing (time permitting)
2	hw2 (general programming) tips You can be less than perfect and still do well Write/think pseudocode before you write Java Submit partial solutions, park on downhill slope Use memo.txt to track problems/solutions If you get help please say so! Naming and prettyprinting conventions matter When UI is specified go for exact match (PhoneBill class) don’t do more than is asked for!
3	new Important Java keyword Use new to create an object: in Bank.java main Bank javaBank = new Bank(“Engulf…”); Think of ordering a Bank from the Bank factory Invokes special method in Bank.java called a constructor Name of constructor is name of class
4	Bank constructor sets value for bankName field creates a Terminal and two BankAccounts (invoking constructors in those classes) 41 public Bank( String name ) 42 { 43 bankName = name; 44 atm = new Terminal(); 45 account1 = new BankAccount ( INITIAL_BALANCE ); 46 account2 = new BankAccount ( INITIAL_BALANCE ); 47 }
5	Linear Equations Truck rental rate: $75 plus $1.15 per mile totalCost = 75.0 + 1.15 * milesDriven Trips by air take 2 hours at the airport and 1 hour for each 400 miles flown: tripTime = 2.0 + (1.0/400.0)flightMiles Temperature conversion: degreesF = (9.0/5.0)degreesC + 32.0 y = m*x + b // common abstraction Model linear equations as Java objects: write general class LinearEquation many applications can use its features
6	Temperature conversion application
7	clients Only method in Temperatures class is main No arithmetic in Temperatures.java class Temperatures is a client for LinearEquation, which provides services Bank is a client for Terminal and BankAccount The client knows only the API application programming interface whatever’s declared public in that class not the implementation (Java details)
8	LinearEquation API Two public constructors public LinearEquation( double m, double b ) public LinearEquation( double x1, double y1, double x2, double y2 ) Two public methods public double compute( double x ) public LinearEquation getInverse() To see how to use these services, look at the javadoc
9	www.cs.umb.edu/joi/latest-joi-cd/ javadoc/2/linear/index.html
10	javadoc Web documentation generated from source Special javadoc comment: /** … */ LinearEquation.java line 53
11	How Temperatures class uses LinearEquation services construct a LinearEquation with new (line 25) 25 LinearEquation c2f = new LinearEquation( 9.0/5.0, 32.0 ); (carefully use 9.0/5.0 to avoid integer division!) send a getInverse message to create another 28 LinearEquation f2c = c2f.getInverse(); send compute messages (lines 36, 38 , not 35, 37 ) 35 terminal.print( "c2f.compute( 0.0 ), should see 32.0: "); 36 terminal.println( c2f.compute( 0.0 ) );
12	Pseudocode for PhoneBill main create a Terminal get basic rate, message unit cost from user create LinearEquation objects you need get number of message units from user compute cost, tell user get amount willing to spend from user compute number of message units, tell user Use Temperatures.java as a template – copy the ideas there, or edit a copy of the file, changing what’s necessary
13	Testing Important Psychologically difficult you don’t want to know if your code is broken when the programming is done you’d like to be done In industry there’s a QA department - consider asking a friend We test your code when we run it. We’re mean. Where is the error? in the code in the documentation in the specification
14	Testing a client class Suppose you’ve written LinearEquation, and it compiles correctly. How can you know it’s right? Need a test driver: main somewhere to test all the public methods in the client Temperatures class tests LinearEquation (Terminal has its own main for testing – try it)
15	Test cases known in advance First part of Temperatures main Tests hard coded (part of program, known at compile time) - no user input Output echoes input (self documenting) Test cases provided by programmer or specification
16	Interactive Tests Second part of Temperatures main Programmer doesn’t know test cases in advance (at compile time) Input provided at run time by user (in CS110 we use Terminal for this) No need for output to echo input
17	Incomplete testing … Temperatures does not test LinearEquation thoroughly enough second constructor (line through two points) never used no stress testing (hard cases – big numbers, negative numbers) Our grading scripts will test all of your code – so you should do it first!