Lets Talk about Smalltalk History of Smalltalk Developed

Let’s Talk about… Smalltalk

History of Smalltalk Developed in the early 70’s (1969) in the Learning Research Group at Xerox’s Palo Alto Research Center Companies who invested in the research and development of Smalltalk: • Xerox • Apple • Digitalk • Object Technology Inc. (OTI) • IBM

Early Beginnings The Xerox Smalltalk Team developed the mouse technology and the bitmap • First graphical bit-map based • multi-windowing (window overlapping) • programming environment (debugger, complier, editor, browser) • with a pointing device

What is Smalltalk? • a TRUE object-oriented programming (OOP) language • Encapsulation • Polymorphism • Inheritance • Data Binding • Integrates a multi-windowed development environment • Simple and Compact Language

What is Smalltalk? a large set of reusable classes (UI, sockets, basic data structures, etc) • • a set of powerful development tools • Browsers • UIBulider • Inspector • Crash recovery • Project Management A run-time environment based on virtual machine technology •

Smalltalk language • Everything is an object (numbers, files, editors, compliers, points, tools, boolean) • All actions are done by sending a message to an object OR Objects communicate ONLY by message passing • Every object is an instance of a class (which is also an object)

Object, Class, Methods OBJECT • An object is a collection of data and code CLASS • A class is the definition of an object • The class of an object holds the code for the object • Each class defines data and a set of methods (the code) which operates that data METHODS • Methods always belong to a class • A method in Smalltalk is a subroutine • It takes at least one parameter and always returns one value

Object, Class, Methods Class Object • Data • Methods (subroutine) to operate data Messages Class Object Messages • Data • Methods (subroutine) to operate data Class Object • Data • Methods (subroutine) to operate data

Messages Objects communicate through messages… Message 1 + 2 • receiver: 1 (an instance of Small. Integer - Object) • selector: #+ • arguments: 2 (an instance of Small. Integer - Object) Message Workstation with. Name= #mac • receiver: Workstation (a class) • selector: #with. Name • arguments: #mac

Syntax Differences C++ / Java Small. Talk Comments /*comments*/ //comments “comment” Assignments int max=100; Variable : = avalue Basic Types “string” ‘string’ Self Reference this. get. Class() self class

Smalltalk vs Java & C++ Smalltalk • “Everything is an object” • Objects are passed by reference • Objects are the units of encapsulation C++ • “Everything is a structure” • Objects are passed by value (pointers) • Classes are the units of encapsulation Java • “Almost everything is an object” • Objects are passed by reference (no pointers) • Classes are the units of encapsulation (like C++)

Alan Kay Smalltalk addressed the need for a small, highspeed, PC-based product The major ideas in Smalltalk are credited to Alan Kay “making simple things very simple and complex things very possible” – Alan Kay

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