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

Computer Vs Program Model CPU Program Compiler ???

Structuring in Scripts Speech IntroductionConclusionBody Paragraph 1Paragraph 2 Sentence 1Sentence 2 Script components are abstract So are program components

Manufactured ObjectsNatural Objects Program Components ~ Physical Objects ~ Program Objects

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

Classification through Factories manufactured by

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

A Simple Class public class ASquareCalculator { public int square(int x) { return x*x; }

2.2 Nature of a Function Domain/Parameter Values Range/Result Values Mapping

Mathematics Vs Java Function Syntax Inspiration for Functional Languages square: I  I square(x) = x 2 Mathematics public int square(int x) { return x*x; } Java

Instantiating ASquareCalculator

ASquareCalculator Instance

Invoking a Method

ABMICalculator Body Mass Index weight height 2 (kg) (metres) public class ASquareCalculator { public int square(int x) { return x*x; } 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

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 Reboot! previous classpath current directory jar files may be zipped

Check After Reboot

Developing BMI Program

Interacting with ObjectEditor

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

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

Formal Vs Actual Parameters parameters actual public double calculateBMI(double weight, double height) { return weight / (height*height); } parametersformal Invoke method weight 0 height 0 variablesmemory assigned

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

Class Access Error

Method Access Error

User Error

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' Line no char. no

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