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 ConclusionBody

Paragraph 1 Paragraph 2

Sentence 1 Sentence 2

Script components are

abstract

So are program components

Manufactured Objects

Natural Objects

Program Components ~ Physical Objects

~ Program

Objects

Program Objects ~ Manufactured Objects

Program

Object

add

subtract

methodsexecuteinvokecall

manufactured byaccelerate

brake

operations

perform

Classinstance of

Program

Object

Classification through Factories

manufactured by

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/ParameterValues

Range/ResultValues

Mapping

1

42

3

1

9... ...

Mathematics Vs Java Function Syntax

Inspiration for Functional Languages

square: I Isquare(x) = x2

Mathematics

public int square(int x) {

return x*x;}

Java

Instantiating ASquareCalculator

ASquareCalculator Instance

Invoking a Method

ABMICalculator

Body Mass

Index

weight

height2

(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

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 ClasspathSET 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

Interacting with ObjectEditor

Program Development ProcessText Editor

ABMICalculator Source Code

creates

Java Compiler

reads

ABMICalculator Object (Byte) Code

creates

Java Interpreter

ABMICalculator Instance

calculateBMI

instantiates calls

ObjectEditor

main

calls

ClassHeader

ClassBody

Anatomy of a Class

2.

3.

4.

5.

6.

7.

{

{

}

1.

}

AccessSpecifier

public class ABMICalculator

MethodHeader

Method Body

public double calculate BMI(double weight, double height

ReturnType

ReturnStatement

return

ReturnExpression

weight/(height*height);

ParameterName

Parameter Type

Formal Vs Actual Parameters

parametersactual

public double calculateBMI(double weight, double height) {

return weight / (height*height);}

parametersformal

Invoke method

weight 0

height 0

variables memory

assigned

74

1.77

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

User Error

JVC Error Reporting

ABMICalculator.java (3,3) : error J0232: Expected '{' or ';'ABMICalculator.java (3,3) : error J0021: Expected type specifierABMICalculator.java (3,3) : error J0019: Expected identifierABMICalculator.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