Computer Programming with GNU Smalltalk - Free

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54 Computer Programming with GNU Smalltalk My brain: it's my second favorite organ. Woody Allen
Objects, Messages and Classes: Part II 55 Chapter 5: Objects, Messages and Classes: Part II Encapsulation Inheritance Ever wondered how the electronic circuits inside your cell phone works? Ever needed to know that? Most probably not. Because, we don't need to know all the manufacturing details about our cell phone to use it. Just reading the manual is enough to use all of its features. So, we cannot know all details, all scientific laws, all properties of an object we use and we don't need to. Object oriented programming introduces encapsulation concept to apply this real life fact in our applications. Smalltalk does not allow you to directly modify internal state of an object. Objects can only be communicated by sending messages to them. So, Smalltalk encapsulates the unnecessary information. Beside encapsulation allows us to think in a real world manner, it also provides some kind of information hiding which helps our program to be solid and reusable. This means, if you hide an object's implementation from the programmer and provide him/her just a protocol to communicate with that object then the programmer won't be affected by implementation changes made in the future as long as the protocol is preserved. For example, you created a Calculator class which is able to calculate the roots of a second degree equation. You just send the equation's information to it and it returns the roots... Maybe it uses an inefficient algorithm which causes it to calculate the roots in hours. But, well, it is better than nothing and you distributed the code to friends (we shall call them clients). Maybe, after distribution, you found a revolutionary approach which reduces the calculation time into seconds. The algorithm is changed but the protocol does not need to because the clients just need to provide the equality to the calculator and want it to solve the equation. How calculator solves the equation is not their business. So you can benefit the advantages of encapsulation and distribute your new code to clients. Clients just need to replace the Calculator class and does not need to change their own program. Human beings like categorizing things. Because categorizing brings order and order brings easymanipulation. Similar elements come together to form groups (or categories) and some special properties of them are the thing which distinguishes them from other group members. We may group some groups together, according to their similarities to form some other groups and also group them to form other groups. This process can go on until we reach one main group which is an ancestor of all others. This is actually a simulation of life itself. The elements we mentioned above are objects and the groups are classes. What is the most general expression we use for elements? The answer is object. We can call everything as an object and then derive a special kind of object from it to which we give names like car, house, animal etc. But remember, we call objects which we use to create instances as classes. So, when we say car, house,
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Computer Programming using GNU Smal
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To the ant I accidentally crushed y
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II We will often use this kind of b
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Contents Preface I Who is This Book
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Postface 107 About the Author......
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Chapter 1: Introduction to Programm
Page 15 and 16: Away f rom Hardware Easy -to-Mainta
Page 17 and 18: Introduction to Programming World 5
Page 21 and 22: like image viewer or PDF reader to
Page 25 and 26: Chapter 2: Introduction to GNU Smal
Page 27 and 28: Introduction to GNU Smalltalk 15 me
Page 29 and 30: Introduction to GNU Smalltalk 17 4.
Page 31 and 32: Objects, Messages and Classes: Part
Page 33 and 34: Unary, Binary and Keyword Messages
Page 37 and 38: Common Classes and Their Usage: Par
Page 43 and 44: setNumerator:setDenominator: Object
Page 47 and 48: Carl tellUsYourLastName Here Carl r
Page 51 and 52: aSet Set ('Soap' 'Toothbrush' ) Obj
Page 53 and 54: new We create a dictionary with new
Page 57 and 58: Chapter 4: Controlling the Flow of
Page 59 and 60: anObject ifTrue: [block-expression-
Page 61 and 62: Controlling the Flow of Execution 4
Page 63 and 64: ] This is the 1. line. This is the
Page 65: Controlling the Flow of Execution 5
Page 71 and 72: The general syntax for creating cla
Page 75 and 76: ourObjectName := SubclassName new O
Page 77 and 78: ] ] 'Woof!' printNl. Animal subclas
Page 79 and 80: Animal setAnimalNumber: 1. dog setN
Page 81 and 82: printString, ' years old.'; cr. ] ]
Page 83 and 84: me := Human new. me setName: 'Canol
Page 85 and 86: getAge [ ^age ] Objects, Messages a
Page 91 and 92: Chapter 6: What to Do Next How Can
Page 93 and 94: What to Do Next 81
Page 95 and 96: Installing Programming Environment
Page 97 and 98: ./configure make make install Insta
Page 99 and 100: Appendix B: ASCII Table Number (Dec
Page 101 and 102: Appendix C: Answers of Review Quest
Page 103 and 104: Chapter 2 Answers of Review Questio
Page 105 and 106: value, directly. Answers of Review
Page 107 and 108: Answers of Review Questions 95 exam
Page 109 and 110: ]. Transcript cr. Answers of Review
Page 111 and 112: 2. called inheritance. Encapsulatio
Page 113 and 114: setHonesty: rateOfHonesty [ "Honest
Page 115 and 116: Answers of Review Questions 103 of
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Alphabetical Index accessor 66 Argu
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Postface Postface 107 Now, we are a
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