Exploring Object-Based Programming: Intuitive Explanation & Concrete Examples

Object-based Programming • Intuitive explanation • Two concrete examples • Calculators • addition • BMI • Programming Environment

Computer Vs Program Model CPU Program ??? Compiler

Structuring in Scripts Speech Introduction Body Conclusion Paragraph 1 Paragraph 2 Script components are abstract Sentence 1 Sentence 2 So are program components

Natural Objects Manufactured Objects Program Components ~ Physical Objects ~ Program Objects

operations manufactured by accelerate perform brake add instance of Class subtract execute Program Object invoke methods call Program Objects ~ Manufactured Objects Program Object

Classification through Factories manufactured by manufactured by

Classification through Classes instance of ASquareCalculator ASquareCalculator Instance ASquareCalculator Instance instance of ABMICalculator ABMICalculator Instance ABMICalculator Instance

A Simple Class publicclass ASquareCalculator { publicint square(int x) { return x*x; } }

2.2 Nature of a Function Domain/Parameter Values Range/Result Values 1 1 2 4 3 9 ... ... Mapping

Mathematics square: I  I square(x) = x2 Java publicint square(int x) { return x*x; } Mathematics Vs Java Function Syntax Inspiration for Functional Languages

Instantiating ASquareCalculator

ASquareCalculator Instance

Invoking a Method

weight (kg) Body Mass Index height2 (metres) publicclass ASquareCalculator { publicint square(int x) { return x*x; } } ABMICalculator public class ABMICalculator { public int calculateBMI (int weight, int height) { return weight/(height*height); } }

Bare Bone Environment • MS-DOS Prompt (Command Interpreter) • Notepad (editor) • Jvc (J++ compiler) • Jview (J++ interpreter) • ObjectEditor

Creating MS-DOS Prompt Window

Using Notepad to Edit Autoexec notepad C:\autoexec.bat

Setting Path and Classpath • Path • List of Command Directories • Must have Jvc and Jview Directories • Class Path • List of Library Directories, Jar Files, Zip Files • Add oe.jar, shapes.jar, swingall,jar

previous classpath current directory jar files Reboot! Setting Path and Classpath SET PATH=%PATH%;C:"\Program Files\Microsoft Visual Studio\VJ98" SET CLASSPATH=%CLASSPATH%;.;D:\Java\lib\oe.jar;D:\Java\lib\shapes.jar;D:\Java\lib\swingall.jar may be zipped

Check After Reboot

Developing BMI Program

Interacting with ObjectEditor

creates ABMICalculator Source Code ABMICalculator Instance reads Java Compiler calculateBMI creates calls instantiates ABMICalculator Object (Byte) Code ObjectEditor main calls Program Development Process Text Editor Java Interpreter

Method Header Method Body Class Header Class Body Parameter Type Parameter Name Access Specifier Return Type Return Statement Return Expression Anatomy of a Class 1. public class ABMICalculator 2. { public double calculate BMI(double weight, double height 3. 4. { return weight/(height*height); 5. } 6. 7. }

Invoke method variables memory weight 0 height 0 1.77 Formal Vs Actual Parameters publicdouble calculateBMI(double weight, double height) { return weight / (height*height); } formal parameters assigned actual parameters 74

Syntax Error Semantics Error Logic Error Access Error Errors class ABMICalculator { double calculateBMI(double weight, double height) { return (height*heigh)/weight }

Class Access Error

Method Access Error

User Error

Line no char. no JVC Error Reporting ABMICalculator.java (3,3) : error J0232: Expected '{' or ';' ABMICalculator.java (3,3) : error J0021: Expected type specifier ABMICalculator.java (3,3) : error J0019: Expected identifier ABMICalculator.java (5,1) : error J0020: Expected 'class' or 'identifier'

Case Conventions • Start variable name with lowercase letter (weight). • Start class name with uppercase letter (ABMICalculator) • Start each new word with upper case letter (ASquareCalculator)

Object Editor Changes Case calculateBMI()

Identifiers • Reserved Words/KeyWords • double, class, int, public, return • boldface • Programmer-defined Names • Variable Names • Class Names • First character is letter • Other characters:letter, digit, _ • calculateBMI2 • calculate_BMI

Exploring Object-Based Programming: Intuitive Explanation & Concrete Examples

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