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 • Object Technology Inc. (OTI) • Apple • IBM • Digitalk

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 Messages Class  Object Class  Object Data Methods (subroutine) to operate data Data Methods (subroutine) to operate data Messages

Messages Objects communicate through messages… Message  1 + 2 • receiver: 1 (an instance of SmallInteger - Object) • selector: #+ • arguments: 2 (an instance of SmallInteger - Object) Message  Workstation withName= #mac • receiver: Workstation (a class) • selector: #withName • arguments: #mac

Syntax Differences C++ / Java SmallTalk Comments /*comments*/ Assignments int max=100; Variable := avalue Basic Types “string” ‘string’ Self Reference this this.getClass() self 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, high- speed, 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

…..Thanks for listening…..