1	CS110 Lecture 2 January 29, 2004 Announcements hw1 part 1 – due right now hw1 part 2 – due Tuesday night Questions Agenda turnin Object oriented programming (bank simulation) XEmacs
2	Questions Do ask in class when you have come with a question are a little confused think I have made a mistake think others might learn from your question/insight Don’t ask just to show off if you are completely lost (come see me instead) if you haven’t read the book and hw and your email what happened in a class you missed after class about something in the class
3	email etiquette (please) Ask (in email) after you have tried to solve your problem, but before you’ve wasted 8 hours stuck in one place with enough detail so that I can help Don’t expect immediate feedback I may cc question and answer to class Do correspond with your friends No junk mail
4	Electronic hw submission turnin system: http://turnin.cs.umb.edu/ (available by Monday, perhaps sooner) Instructions: follow link on course web page Your user name (all lower case) up to 6 characters from last name balance to 8 characters from first name John Kennedy ® kennedjo Clark Kent ® kentclar Wei Liu ® liuwei Password: passwd (change it!)
5	Object oriented programming The (software) world consists of objects Each object is an instance of a class An object has fields that describe what it looks like (its state) methods that describe how it behaves One object sends a message to another asking it to use one of its methods to do some work Add italicized words to your vocabulary Illustrate these abstractions with bank example in Java
6	OOP in Java File BankAccount.java describes BankAccount objects (instances of class BankAccount) BankAccount.java has two audiences people (programmers like us) the Java compiler Java files always start with comments a convention good programs honor not a rule in the Java language, but a rule for us Comments are for people to read: Java doesn’t care // text up to end of line is a comment /** special javadoc comment – more later / / old style comment– rare */
7	BankAccount.java
8	fields : what an object looks like Each field has a type, a name and a value BankAccount object picture Code in BankAccount.java tells type (int, for integer) and name (balance – good choice by programmer) Value (999) may change from time to time
9	Bank object’s fields (picture)
10	Bank object’s fields (code) From Bank.java, showing types and names of four fields type name 22 private String bankName; // Bank’s name 23 24 private Terminal atm; // talks to customer 25 26 private BankAccount account1; 27 private BankAccount account2; Conventions: Class names always begin with an upper case letter Field names always begins with a lower case letter If type is a class then value is that kind of object
11	Messages Ask an object to work for you: send it a message Bank.java (line 116) account.deposit(amount) this Bank object sends a deposit message to object account of type BankAccount Java syntax: object.message(info) syntax: what the program looks like on the page deposit method in BankAccount.java does the work
12	methods : how an object behaves BankAccount has several methods: deposit (int amount) // line 47 add amount to current balance, changing value of balance field getBalance( ) // line 58 tell whoever sent the message how much money is in this account (value of balance field) balance does not change the empty parentheses tell us this method needs no information from the sender to do its job
13	Messages (reprise) Ask an object to work for you: send it a message Bank.java (line 126) atm.println(“sorry, . . . ”) this Bank object sends a println message to object atm of type Terminal asking it to print a String on the screen Java syntax: object.message(info) println(String something) method in Terminal.java does the work Trust Terminal.java to do the right thing
14	Message invoking a method
15	Homework 1 Part 1 (hard copy due right now) Play with Bank simulation Part 2 (collected electronically Tuesday night) Play with Bank simulation Improve the Bank simulation Write about your coding and testing
16	emacs is a programmer’s editor prettyprint tab, java ® indent compile ctrl-x ctrl-m tools ® compile ® compile loop through compiler errors ctrl-x ` (backquote) tools ® compile ® next error run programs ctrl-x ctrl-r tools ® shell ® shell learn from XEmacs/Java tutorial