Student Originated Software 1997-1998 Fall Quarter
		A Software Engineering Course at The Evergreen State College

Student Originated Software 1997-8 Object-Oriented Programming (Smalltalk) Lecture 2a last time: programming language paradigms.... selecting a programming language for a project.... selecting a language _to teach_ distinguish concept, ability, skill why OO? why smalltalk? objects what's an object: code + data methods encapsulate variables invoking methods? objects send, receive messages; sender, receiver; what's a class? defining objects - classes and instances inheritance, overriding, polymorphism (next week) using oo models for software development - modeling the real world! the language.... naming conventions - height, myHeight; Book, aBook; Employee, anEmployee literals (constants) 8r377, 16rFF,1.586e5,$a,#(1,2,3),#[1,2,3] variables sending messages every message expression has a value. unary, binary, keyword; left to right. list addFirst: newComponent list removeLast ages at: 'Brett' put:3 address at: 'Peggy' HouseholdFinances spend:32.50 on: 'utilities' 1+2*3 2*theta sin (2*theta) sin frame scale: factor max:5 frame scale: (factor max:5) bigFrame width:smallFrame width*2 p.22 combining messages (chaining, cascading) (book openAtPage: 1+2*3) print most methods return self, usually by default, but not always! block - a deferred sequence of messages - evaluated when the block receives the message aBlock := [a:=0]. aBlock value MyBlock := [:anObject | anObject print]. anotherBlock := [:parm1 :parm2| |tmp| tmp := parm1 incorporate:parm2. tmp := rehash. ] executing blocks MyBlock value: 'This is a string sent to print'. value, value:, value:value:, value:value:value: valueWithArguments:argArray (> 3 arguments. classes attributes (class and instance variables) methods (class and instance methods) Object subclass #SpendingHistory instanceVariableNames: 'cashOnHand expenditures' classVariableNames: ' ' poolDictionaries: ' ' category: 'Spending' that's all there is to the language! ---------------- the smalltalk virtual machine interprets code as it comes in "the image" -- where code and object instances are stored the Smalltalk Virtual Machine (your image is its memory) the development environment (your classes + class library) files - virtual image sources visual.sources (base) image visual.im (your) image myvisual.im changes file mycode.changes file-ins mycode.st ----------- advice: smalltalk learning curve be prepared for culture shock (not the waterfall model!) start off small explore and work interactively be prepared to throw code away get some help -- ask the lab aids work with your partner! (come to help sessions - if/when we have some) check out the smalltalk FAQs and listservs ---------------- about visual works (minimal subset) launcher (aka main window, transcript) workspace browser (to look at classes) demo - in class   launcher, main window (aka transcript)   workspace select function (editing), operate function (undo, do it, inspect SAVING YOUR IMAGE....file-out-as #(1 2 'three') "inspect it" | array1 array3 array2 | array1 := #(1 2 'three'). array3 := array2 := array1. array1:= #[6 7 8]. array2:= #[3 4 5]. array1 inspect. array2 inspect. array3 inspect. ---------- Application Development The system browser! its panes: class categories, classes, protocols, methods, in Lab - Today, we will do Chapter 6 & 7. add a new method to an existing class (Number) diff:aNumber "return the absolute difference between me and aNumber" | temp | temp := self - aNumber. temp < 0   ifTrue:[^temp negated]   ifFalse:[^temp] diff:aNumber "return the absolute difference between me and aNumber" ^(self - aNumber) abs some useful browsers and menu operations.....   system browser   class browser   hierarchy   implementors of --------- A small application (Spending) new category, with classes & methods). self new initialize self new setInitialBalace:anAmount ^self new setInitialBalace:anAmount setInitialBalance: anAmount cashOnHand := anAmount. expenditures := Dictionary new. totalSpentOn: reason (expenditures includesKey: reason)   ifTrue:[^expenditures at:reason]   ifFalse:[0] spend:anAmount on:reason expenditures   at: reason   put: (self totalSpentOn: reason) + anAmount. cashOnHand := cashOnHand - anAmount. printOn:aStream super printOn:aStream. aStream space. aStream nextPutAll: 'balance:' cashOnHand printOn: aStream. expenditures keysAndValuesDo: [:reason :amount | aStream cr.   reason printOn: aStream.   aStream tab.   amount printOn: aStream] invoking the app:   mySpendingHistory initialBalance:600   mySpendingHistory spend:1000 on: 'rent'. Saving your source code   file out as ... Spending.st using the file browser, 'spawning' a new (file) broswer [ SOS Home Page | Case Study | Year Long Projects | OOP ]