Object Oriented Programming (OOP) Overview CS61A Lecture 14

Transcription

1 Objet Oriented Programming (OOP) Overview CS6A Leture Colleen Lewis Multiple independent intelligent agents Message passing, loal state, inheritane define-lass, instantiate, ask, method, instane-vars, lassvars, self, usual, parent???? & Sheme keywords Class like a blueprint of an objet define-lass a partiular objet something you an ask an instane of a lass to do. method ask s The doubler lass (define-lass (doubler) (se stuff stuff))) name body Class name argument variable Creating objets & alling methods STk> (define d (instantiate doubler)) d Call a method On this instane of a lass Call this method STk> (ask d 'say '(how are you?)) (how are you? how are you?) Class name Creates an instane of a lass With this argument

2 Modify the doubler lass (define-lass (doubler) (se stuff stuff))) STk> (ask d 'add 3) 0 STk> (ask d 'add ) 4 add is a: A) funtion B) method C) lass D)message instane variables instane-vars Instane variables variables loal to an instane of a lass instane-vars instane-vars Instane variable name (instane-vars (ount 0) ) Initial value Could add another Create these variable here. E.g. variables for eah (x 3) new instane (method (welome) Can be aessed (se 'my 'ount 'is ount))) When do you use quotes? (instane-vars (ount 0)) (method (welome) (se 'my 'ount 'is ount))) STk> (define (instantiate? ounter)) STk> (ask?'welome) (my ount is 0) Whih needs a quote? A) Class name B) method name C) both D) neither If you hange the lass, ALWAYS rereate your objets STk> (load "let4.sm") okay STk> (define (instantiate ounter)) STk> (ask 'welome) (my ount is 0)

3 Aessing instane variables (instane-vars (ount 0) (x 3)) (method (welome) (se 'my 'ount 'is ount))) set! STk> (define (instantiate ounter)) STk> (ask 'ount) 0 STk> (ask 'x) 3 s for instane variables are provided automatially Non-funtional programming (A way to hange instane variables) Changing instane variables STk> (define (instantiate ounter)) STk> (ask 'ount) 0 STk> (ask 'next) STk> (ask 'next) STk> (ask 'ount) Changing instane variables (instane-vars (ount 0)) Variable to (method (next) hange (set! ount (+ ount )) ount)) Non-funtional programming so you may do many things New value in one method. Sheme returns the last one Add a method addx (instane-vars (ount 0) (x 0)) (method (next) (set! ount (+ ount )) ount)) STk>(ask 'next) STk> (ask 'addx 0) STk> (ask 'x) 0 What was the argument name in your addx method? A) x B) argx C) y D) None used Conept: Loal State 3

4 STk> (define (instantiate ounter)) STk> (define (instantiate ounter)) STk> (ask 'ount) 0 STk> (ask 'next) STk> (ask 'ount) s ount wasn t hanged Class variables Uses the keyword lass-vars Instane variables variables loal to an instane of a lass instane-vars Class variables variables shared by all instanes of a lass lass-vars STk> (define (instantiate ounter)) STk> (define (instantiate ounter)) (ount: total: ) (ount: total: ) total is a lass variable shared by all instanes of the lass (ount: 3 total: 3) What will this print? STk> (ask 'next) A(ount: total: 4) B(ount: total: ) C(ount: 4 total: 4) D(ount: 4 total: ) Class variables in Sheme OOP (instane-vars (ount 0)) (lass-vars (total 0)) (method (next) (set! ount (+ ount )) (set! total (+ total )) (se 'ount: ount 'total: total))) Counter objets respond to the message 'total Instantiation Variables 4

5 Instane variables variables loal to an instane of a lass instane-vars a partiular objet Instantiation variables arguments provided when we reated the instane of the lass. (define-lass (beah-bum name) (instane-vars (surfs #t))) Instane variable STk> (define surfer (instantiate beah-bum 'bob)) surfer STk> (ask surfer 'name) bob STk> (ask surfer 'surfs) #t Instantiation variable Created differently but they work the same way Write the meet method STk> (load "let4.sm") okay STk> (define surfer (instantiate beah-bum 'bob)) surfer STk> (ask surfer 'meet 's6a-lass) (hi s6a-lass my name is bob dude) 's6a-lass is the value of an A) instane variable B) instantiation variable C) method argument The initialization keyword A way to initialize lass variables. surfer-names is. STk> (define s (instantiate beah-bum 'bob)) s STk> (ask s 'surfer-names) (bob) STk> (define s (instantiate beah-bum 'jim)) s STk> (ask s 'surfer-names) (jim bob) A) An instane variable B) An instantiation variable C) A lass variable D) Something else Class Instane variables Instantiation variables Class variables 5

6 Initializing lass-vars (define-lass (beah-bum name) (set! surfer-names (se name surfer-names))) (se stuff 'dude))) This is the FIRST initial value (lass-vars (surfer-names '())) If other instanes of We already knew the lass already how to make lass exist, do this variables (initialize SOLUTION Modify the doubler lass (define-lass (doubler) (se stuff stuff)) name arguments (method (add num num) (* (+ num num)))) body Solution addx (instane-vars (ount 0) (x 0)) (method (addx argx) (set! ount (+ ount argx)) (set! x argx) ount)) I don t want the argument to be named x b/ then I would need to write (set! x x) meet solution (define-lass (beah-bum name) (instane-vars (surfs #t)) (method (meet someone) (se 'hi someone 'my 'name 'is name 'dude))) Class like a blueprint of an objet define-lass a partiular objet something you an ask an instane of a lass to do. method ask Instane variables variables loal to an instane of a lass instane-vars a partiular objet Instantiation variables arguments provided when we reated the instane of the lass. Class variables variables shared by all instanes of a lass lass-vars 6