Introduction to Object-oriented Programming in Smalltalk

Size: px

Start display at page:

Download "Introduction to Object-oriented Programming in Smalltalk"

Edith Weaver
5 years ago
Views:

1 Introduction to Object-oriented Programming in Smalltalk 1

2 Objects are responsible for their own actions! In procedural programming, I write code that reaches into the internals of some data structure and twiddles with the bits string process reads/ writes process reads/ writes process reads/ writes 2

3 In O-O programming, I politely request some other object to perform some work on my behalf, and it politely answers me String copy print concat 3

4 In O-O programming, I politely request some other object to perform some work on my behalf, and it politely answers me String Encapsulation boundary copy print concat 3

5 In O-O programming, I politely request some other object to perform some work on my behalf, and it politely answers me String Encapsulation boundary copy print concat copy 3

6 In O-O programming, I politely request some other object to perform some work on my behalf, and it politely answers me String Encapsulation boundary copy print concat 3

7 In O-O programming, I politely request some other object to perform some work on my behalf, and it politely answers me String Encapsulation boundary copy print concat anewstring 3

8 In O-O programming, I politely request some other object to perform some work on my behalf, and it politely answers me String Encapsulation boundary copy print concat 3

9 Computation as Simulation This collection of autonomous objects is like the world of discreet event simulation Anthropomorphize! It s OK to think about this object talking to that object... In fact, it s recommended 4

10 Programming Philosophy Object-Oriented programming is programming by simulation. The algorithm is less important than the structure of the solution. When requirements change: If the structure represented the structure of some reality, then the new requirements will be consistent in that reality. Object-oriented design is the search for this structure: uncover the structure rather than construct in isolation. 5

11 Shopping vs. Building Constructing an Object-oriented application is a process of shopping for the components that one needs occasionally we add a new item to the shelf. usually we can find a component that almost fits. The openness of an OO language allows the programmer to change the component that almost fits into one that is a good fit. works only if we have a rich set of components on the shelf, and if they are open to change. 6

12 Is this the only view of OO Programming? No! People disagree on the meaning and role of: 1. Encapsulation 2. Types 3. Inheritance 4. Polymorphism 5. Sets and classes 7

13 Smalltalk Squeak is an open-source version of Smalltalk. Smalltalk is still the best example of a Pure O-O language The Squeak workspace is a place in which you can create and interact with objects. Large and active community of contributors Runs bit identical on just about any platform, including many PDAs 8

14 9

15 "#$!%&'$()!*+,-. Yes, you are... LIVE in MORPHIC x S q u e a k Text morphs can be chained together, causing their contents to flow between containers as m ha t the contents or the containers orp t of change. If a TextMorph is h. pe embedded in another If th a morph, then you canask e to have itfill thesh te xt is embedded in a curve, then you can ask to have the text follow that curve, as illustrated in this image. You can also ask to have the text avoid occlusions, in which case it will do its XII XI I best to avoid Text sibling submorphs in this X II that are in front of it. Kerning rectangle (cmd sh + or -) can flows help with the IX III awkward spacing around that results from narrow margins. me VIII IV Other morphs can also be embedded in text as glyphs. VII V VI Embedding placement is based on the top left corner of the morph s bounding box. T o o l s S u p p l i e s %&'$()!89 /0(1$ #+2:!;% 61++./$27 2+',3$2!4!3#(51$2 10

16 "#$%%&$%'!"()&$* 6 7#!89.5*:!$#1!24*88)8;!0*2+*<)8;!etc. = >4*88!21)*5?#.!*.@!3)5A#@!2*5)<#1?B*5?#.!*1)!@#.)! imperatively!(8?.<!5a)!@)c)4#03).5!5##48 6 DA)!3)5A#@!89.5*:!?8!8?304);!E(5!@?$$)1).5 +,!$"&-.)/! F-.8G)1!GA)5A)1!5A)!1)2)?C)1!8#158!*$5)1!#1!)'(*4!5#! K!I8)4$!2#30*1),!8)4$!G?5A,!*&51?.<!2#44*5)@,!-82??/1@)1J!LM!N 11

17 786*2+5!09:*36; "#$%%&$%'!(!)*+!,$-./$.+ #< =>*!)/8()*!$9:*36!#< D+!;628/BD E2*()*;6 K2 ;+4*!+;!+9$C* +!;628/B 6>*!;F49$5!request. G6!8;!)/8()*H!6I$!;F49$5;! I86>!6>*!;+4*!/+4*!J*/$6*!6>*!;+4*!$9:*36 6>*!;8/B5*!3>+2+36*2!r 3$/6+8/8/B!+/!8/6*B*2N!+!!$+6N!+/J!+!;628/B 12

18 !"#$%#&'("))*&") 7/+28#9*::+;*#</$#+2;)4*/6:= #E#12?/6'62?/; 2*3*?J*2 <6+2;*6#$%#4*::+;*= :*5*36$2 > C *D+415*:-## "#%+36$2?+5 # E#/*;+6*A# F3#+:G/6*;*2 C /$6*-#/$#3$5$/#+6#6H*#*/A#$%#6H*#:84I$5 13

19 67.*18#9)::*;)#<$.)#*1;(3).5=> D##H#G 1)2)7K)1 :)4)25$1 *1;(3).5? B#C#D i G#H#I!B#JJ#I!B#J#I 3)::*;)#= 5##:).5#5$#$EF)25#B 3)::*;)#+ 3##:).5#5$#$EF)25#G 3)::*;)#// 3##:).5#5$#7.5);)1#$EF)25#!B# <1):(45#7:#D> 3)::*;)#/ 3##:).5#5$#7.5);)1#$EF)25#!B# <1):(45#7:#######> i 14

20 67.*18#9)::*;)#<$.)#*1;(3).5=> D##H#G 1)2)7K)1 :)4)25$1 *1;(3).5? B#C#D i G#H#I!B#JJ#I!B#J#I 3)::*;)#= 5##:).5#5$#$EF)25#B 3)::*;)#+ 3##:).5#5$#$EF)25#G 3)::*;)#// 3##:).5#5$#7.5);)1#$EF)25#!B# <1):(45#7:#D> 3)::*;)#/ 3##:).5#5$#7.5);)1#$EF)25#!B# <1):(45#7:#######> i Not exactly; i is not an object. It's a variable that's bound to an object 14

21 7*89$2:#;*<<+=*<# > BCD#"#E#F#!!G#+6-#H =+4*#4$I*%2$4-#1J/.#6$-#1J/K#)<J/=-#1J/L "#M*69**/-#N#+/:-#F > OP*#3$5$/#Q!R#J/:J3+6*<#6$#6P*#1+2<*2#6P+6#+/# +2=)4*/6#%$55$9<#6P*#,*89$2:S 15

22 !"#$"%&'%()*+,*-.&/ 7 89*#2*3*:;*2#<$2#+/#+2=)4*/6>#3+/#?*# +/$69*2#:/;$3+6:$/#<4*@@+=*#*A12*@@:$/> 7 B;+5)+6:$/#$2C*2#:@ D 1+2*/69*@:E*C#:/;$3+6:$/@ D )/+2F#:/;$3+6:$/G#*;+5)+6*C#left to right D?:/+2F#:/;$3+6:$/@G#*;+5)+6*C#left to right D,*FH$2C#:/;$3+6:$/@ 7 I$#J12:$2:6:*@K#%$2#1+26:3)5+2#$1*2+6$2@ D!#C$*@#/$6#?:/C#4$2*#6:=965F#69+/#L 16

23 !"#$"%&%'(&##")&#'*#+,-"$-.$'#/)"01 +/.22+7#+6-#!#1)6-#89 # +/.22+7#+6-#:#1)6-#!!9 # +/.22+7#+6-#;#1)6-#!;9 < =>?@#3+/#A*#+AA2*B?+6*C#+@ +/.22+7#+6-#!#1)6-#8J#+6-#:#1)6-#!!J#+6-#;#1)6-#!;# 2*3*?B*2#%$2#+55# ;#4*@@+E*@ K2*3*?B*25*@@#4*@@+E*@L < D*@)56#?@#6>+6#$%#6>*#5+@6#4*@@+E*#@*/C =2+/@32?16#@>$F-#GH*55$#I$25CGJ#32 17

24 !"#$"%&'( 7/86+/3*#9+2:+;5*8 < 4+,*#)1#:68#2*12*8*/6+6:$/D < E*35+2*E#:/#6>*#35+88 instancevariablenames: 'name1 name2' =*41$2+2:*8 < F+4*8#5$3+5#6$#+#4*6>$E#;$EG#$2#;5$3, H#student professoratogi#7 18

25 7#!#8#9#: :=!""#$%&'%( ; 4+,*#x# ## /+4*#6<*#$=>*36#2*?)56@/A#%2$4#6<*#*B+5)+6@$/# $%#6<*#*712*??@$/#3 + 5 C#-D#.22+C#/*E-#!FFFFFF ; 4+,*#y#/+4*#+#/*E#!GH#+22+C I J+2@+=5*?#/+4*#$=>*36? ; K<*C#L$#/$6#12$B@L*#?6$2+A*#%$2#$=>*36? I.??@A/@/A#6$#+#B+2@+=5*#4+,*?#@6#/+4*#+# L@%%*2*/6#$=>*36 ; /$#$=>*36#@?#32*+6*L#$2#3$1@*L#=C#+??@A/4*/6 19

26 :";4*<<)<!"#$%&%'()*$" = 2#33*.9@$"8."5A)";4*<<@2*5):#1?"0*.)"#$"*"B1#C<)1 = >?"<)4)258.:"*"3#10A"*.9"2A##<8.:"B1#C<)"3#10A" 24*<<"$1#3"5A)"9)B(:"3).( 20

27 7 89/:9/;#4*6<$:= %9/:*2 > ' ,#A2$D=*E*6<$:=F<$=*G+4*=H$/6+9/-# I=32**/I > ' ,#A2$D=*E*6<$:=F96<'629/;-#I)=*%)5IJ#$2# > <9;<59;<6#+#=*5*36$2J#3<$$=*#9415*4*/6$2=#$%#K# Lcommand-mM#$2#=*/:*2=#$%#KLcommand-nM 21

28 !"#$"#%&'#()*+( &$3)#6.7*4(*84)#1)9$(12)9, : *#>6+6#69#*#>)8965)#><)1)#*.A$.)#69#%1))#5$#2$.5168(5)# <550,DD36..$>E22EC*5)2<E)B(D9'()*+ F 9.*09<$5#*5#<550,DD9> $1E9'()*+90*2)E2$3D : G$2(3).5*56$.H#5(5$16*49H#9>6+69H#$5<)1#965)9H#8$$+9# *.B#0*0)19H#B$>.4$*B9H#*.B#6.%$13*56$.#$.#I 22

29 7 89*#'()*+,#4+:5:/;#5:<6 = +#%2:*/>5?#15+3*#@9*2*#A/*@B:*<C#+2*#4+>*#@*53$4* = <()*+,D2*()*<6E3<F):)3F*>) =.239:G*#$%#HIJKL*<M#HNOPL+/3*4*/6<M#HQ00RJNL< 9661-SS<@:,:F;<);F$2;-TUTUS'VIJKN' = '*+239+B5*#+239:G*#$%#@9$5*#5:< SS;2$)1<F?+9$$F3$4S;2$)1S<()*+, 23

30 Creating Objects in Smalltalk Object are created by sending a message to some other (exisiting!) object called a factory Usually, the factory object is a class, e.g. OrderedCollection new. Array with: 'one' with: 'two' with: 'three'. s := Bag new. The object will be deallocated automatically when it's no longer needed (garbage collected) 24

31 Blocks Blocks are Smalltalk objects that represent Smalltalk code [ ] They can have arguments: [ :x 1 + x ] compare with x. 1 + x Blocks understand messages in the value family: value value: value: value: value: value: value: The Block is not evaluated until it receives a value message 25

32 Examples of Blocks If-then-else is not a built-in control structure: it s a message aboolean iftrue: trueblock iffalse: falseblock discountrate := (transactionvalue > 100) iffalse: [0.05] iftrue: [0.10] You can build your own control structures: ( keyevent controlkeypressed ) and: [keyevent shiftkeypressed] 26

33 Returning an Answer! returns an answer from a method if there is no!, the method returns self! is very useful to return from a block color color ifnil: [!!Color black].! color! in a block returns from the method in which the block is defined - not the method that evaluates the block! 27

34 Arrays Arrays in Smalltalk are Objects They are special in 2 ways 1. there is language syntax to create them #(1 3.4 #symbol) an array literal { /5 asfloat. ('sym','bol') assymbol} a dynamically constructed array Array with: 4-3 with: 17.0/5 with: #symbol the same 2. there are ByteArrays, FloatArrays as well as Arrays 28

35 Characters & Strings Characters are also objects $H is the literal for the character H $H asciivalue is 72 $H digitvalue is 17, $3 digitvalue is 3 collect: creates a new array by applying a function to all elements of the receiver ' ABCDEF' asarray collect: [ :each each digitvalue] evaluates to #( ) 29

36 Other enumeration methods anarray do: ablock applies ablock to each element of anarray, and answers anarray anarray withindexcollect: a2argumentblock answers the new array containing the results of applying a2argumentblock to each element of anarray, together with its index. anarray withindexdo: a2argumentblock 30

37 Examples #(#one #two #three #four) withindexcollect: [ :each :i each,' = ', i asstring] evaluates to #('one = 1' 'two = 2' 'three = 3' 'four = 4') #(#one #two #three #four) withindexdo: [ :each :i Transcript nextputall: each,' = '; show: i; cr] evaluates to #(#one #two #three #four), i.e., the receiver 31

38 Indexing Arrays {#eins. #zwei. #drei} at: 1 {#eins. #zwei. #drei} first {#eins. #zwei. #drei} third {#eins. #zwei. #drei} at: 2 put: #deux modifies the receiver, and answers #deux 32

39 Assignment 1: Whole objects Parse numerals into numbers without using explicit loops or recursion Use the algorithm shown 33

The Smalltalk Environment, SUnit, and Inheritance

Creating Objects in Smalltalk The Smalltalk Environment, SUnit, and Inheritance Object are created by sending a message to some other (exisiting!) object called a factory! Usually, the factory object is