Object-Oriented Programming in PythonGoldwasser and Letscher

Chapter 1:Cornerstones of Computing

Terry Scott

University of Northern Colorado2007 Prentice Hall

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Introduction: Chapter 1 Topics

• Data and types.

• Operations, Functions, and Algorithms.

• Two algorithms for determining the greatest common divisor (GCD).

• High-level programming languages.

• Object-oriented paradigm.

• Designing and modeling.

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Data and Types

• Information is organized data

• Data Types– Built-in types sometimes called primitive

types: most languages have • numbers, • characters, • lists/arrays.

– User-defined types:created by programmer.

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Operations, Functions, and Algorithms

• Central Processing Unit (CPU) – in charge of the computer. Has limited set of instructions.

• Control structures – built into a language to control the order of instruction execution.

• Function – high level behavior created by the programmer.

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Operations, Functions, and Algorithms - Continued

• Abstraction – Functions allow programmer to encapsulate some operation into a chunk of code.

• Algorithms - step-by-step instructions for solving a problem.– Flowchart – graphical display of an algorithm.– Algorithm for finding Greatest Common

Divisor (GCD)

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GCD: Algorithm

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GCD Algorithm (Euclid)

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Euclid's GCDValues for u, v, and r starting with u = 54 and v = 42.

Answer is 6

u v r

54 42 12

42 12 6

12 6 0

6 0

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High Level Programming Languages

• Kinds of Languages.– Low-level programming language:

• Machine code.• Assembly code.

– High-level code:• Python• C++• Many others

• Source Code – code written by programmer that is converted into executable code by compiler or interpreter

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High Level Programming Languages (continued)

• Compiler versus Interpreter– Compiler generates an executable file that

can be run on the computer– Interpreter generates machine code and

executes it immediately one line at a time.

• Syntax versus Semantics– Syntax: rules followed by a language.– Semantics: meaning of statements in a

language.

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High Level Programming Languages (continued)

• Syntax error: when rules of a language are violated. These are found by the compiler or interpreter.

• Semantic error (logic error). Errors not found by the computer.

• Semantic errors lead to incorrect results.

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Object-Oriented Paradigm

• Object-oriented programming (OOP)

• Objects and Classes.– objects are created from classes.– single object from a class is called an

instance.– Data and operations on that data are

encapsulated together. Unit called a class.

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Objects

• Data within a class is called an attribute.

• All attributes together represent the state of an instance.

• Operations contained in a class are called methods.

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Obedient Dog Sequence Diagram

• This and the next slide refer to a diagram two slides ahead.

• Jane and Spot are instances of Person and Dog

• Vertical lines represent chronological lifetime of the instances.

• Solid horizontal lines represent flow of control passing from Jane to spot

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Obedient Dog Sequence Diagram

• Rectangular boxes under Spot represent time passing while operation is being performed.

• Dotted horizontal lines indicate control being passed back to Jane.

• Methods are:– sit( )– liedown( )– rollover( )– fetch( )

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Obedient Dog: Sequence Diagram

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Obedient Dog Fetching Slippers

• Next slide shows a parameter being passed to the fetch() method

• The fetch method expects a parameter telling what to fetch (slippers)

• The dotted horizontal line indicates that redSlippers have been fetched.

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jane invokes: spot.fetch(slippers)

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Instance Methods

• Parameter – how information is passed into a method.

• Return value – how information is passed out of a method.

• The parameters and return value of a method are called its signature.

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Instance Methods

• Kinds of methods:– Accessors or inspectors: method that returns

the value of an instance attribute.– Mutators: change value of instance attribute.– Others

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Television Class

• Diagram on next slide is for a Television class.

• In general these are called class diagrams.

• Upper rectangle lists the attributes of the class

• Lower rectangle lists the methods for the class.

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Television Diagram: Attributes and Methods

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Television Class Design: Methods

• togglePower(): method toggles a switch – pressing flips between on and off.

• toggleMute(): method toggles a switch. TV must be on to have it toggle.

• volumeUp(): changes volume when TV is on and only goes until some maximum volume.

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Television Class Design: Methods (continued)

• volumeDown(): changes volume when TV is on and only goes until some minimum volume.

• channelUp(): changes channel when TV is on and wraps around to lowest channel once the highest channel is reached.

• channelDown() same as channel up but wraps from low channel to high.

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Television Class Design: Methods (continued)

• setChannel(number): changes channel to number if TV is on.

• jumpPrevChan() changes channel to previous channel if TV is on.

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Student Registration System

• Has-a relationships: combination of objects.

• Is-a relationships: inheritance between objects.

• Bob has-a schedule: called composition.

• Design of a student registration system: sequence diagrams on next slides.

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Sequence Diagram for Student Registration System (1st Attempt)

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Student Registration System Sequence Diagram (2nd Attempt)

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Student Registration System Sequence Diagram (3rd Attempt)

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Student Registration System Sequence Diagram (4th Attempt)

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Class Diagrams for Independent Student and Professor

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Student and Professor Inherit from Person

• Student and Professor are both persons.• Common attributes:

– name.– birthdate.– phone number.– current Schedule.

• Student is-a Person and Professor is-a Person.

• Student and Professor inherit from Person.

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Student and Professor Classes Derived from Person

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Drawable Class Diagram

• Next slide shows a drawable class diagram.

• Attributes:– depth.– transformation.– reference point.

• Methods:– rotate.– move.– see others on diagram.

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Drawing Package: Class Diagram

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Proposed Hierarchy of Drawable Objects Showing Inheritance.