Slide 1

Comp 401ObjectsInstructor: Prasun Dewan

#Computer vs. Program Model

ProcessorCompilerProgram (source code)?

#Structuring in ScriptsScriptPerformerTheater

Follows

#Structuring in ScriptsScriptIntroductionBodyConclusionParagraph 1Paragraph 2Sentence 1Sentence 2Script components are abstract.So are program components!

#Program Components ~ Physical ObjectsNatural Objects

Manufactured Objects

~ Program Components

#Program Objects ~ Manufactured Objects

manufacturedbyperform OperationsacceleratebrakeClassProgram ObjectProgram Objectinstance ofMethodsaddsubtractexecute invoke call

#Classification Through Factories

manufacturedbymanufacturedby

#Classification Through FactoriesASquareCalculatorABMICalculatorASquareCalculator InstanceASquareCalculator InstanceABMICalculator InstanceABMICalculator Instanceinstance ofinstance of

#A Simple Instantiated Classpublic class ASquareCalculator {public int square(int x) {return x*x;}}public class SquareCalculatorTester{public static void main (String[] args) { ASquareCalculator squareCalculator = new ASquareCalculator();System.out.println (squareCalculator.square(5)); }}Object CreationObject UseNo static because class will be instantiatedNo package

#Packagespackage math; public class ASquareCalculator {public int square(int x) {return x*x;}}package main; import math.ASquareCalculator;public class SquareCalculatorTester{public static void main (String[] args) { ASquareCalculator squareCalculator = new ASquareCalculator();System.out.println (squareCalculator.square(5)); }}Class in different package must be imported using full name of class ( a la full file name)

#Packagespackage math; public class ASquareCalculator {public int square(int x) {return x*x;}}package math;

public class SquareCalculatorTester{public static void main (String[] args) { ASquareCalculator squareCalculator = new ASquareCalculator();System.out.println (squareCalculator.square(5)); }}Class in same package need not be imported

#Packagespackage math; public class ASquareCalculator {public int square(int x) {return x*x;}}import math.ASquareCalculator;public class SquareCalculatorTester{public static void main (String[] args) { ASquareCalculator squareCalculator = new ASquareCalculator();System.out.println (squareCalculator.square(5)); }}No package means package named default, hence import needed

#Packagespublic class ASquareCalculator {public int square(int x) {return x*x;}}package main;public class SquareCalculatorTester{public static void main (String[] args) { ASquareCalculator squareCalculator = new ASquareCalculator();System.out.println (squareCalculator.square(5)); }}Short name of class in default package same as its full name

#Packagespublic class ASquareCalculator {public int square(int x) {return x*x;}}public class SquareCalculatorTester{public static void main (String[] args) { ASquareCalculator squareCalculator = new ASquareCalculator();System.out.println (squareCalculator.square(5)); }}No package means package named default, hence no import needed here

#Long name with no importpackage math; public class ASquareCalculator {public int square(int x) {return x*x;}}package main;

public class SquareCalculatorTester{public static void main (String[] args) { ASquareCalculator squareCalculator = new math.ASquareCalculator();System.out.println (squareCalculator.square(5)); }}Can use the full name of class directly

#package safemath; public class ASquareCalculator {public long square(int x) {return x*x;}}Why imports/full name?package math; public class ASquareCalculator {public int square(int x) {return x*x;}}package main; import math.ASquareCalculator;public class SquareCalculatorTester{public static void main (String[] args) { ASquareCalculator squareCalculator = new ASquareCalculator();System.out.println (squareCalculator.square(5)); }}Twice the size of intsDisambiguates

#package safemath; public class ASquareCalculator {public long square(int x) {return x*x;}}Amgigous Importpackage math; public class ASquareCalculator {public int square(int x) {return x*x;}}package main; import math.ASquareCalculator;import safemath.ASquareCalculator;public class SquareCalculatorTester{public static void main (String[] args) { ASquareCalculator squareCalculator = new ASquareCalculator();System.out.println (squareCalculator.square(5)); }}Ambiguous

#Why Packages?Can create competing implementations of same class.A la creating files Test.java in different assignment directories/foldersCan browse related classesA la browsing through all files in an assignment directory/folder.Like directories/folders packages can be hierarchicalpackage math.power;public class ACubeCalculator {}

#Browsing Java Classes

Very useful package

#Language vs. Library

Built-in classes

#Changing Parameterpublic class ASquareCalculator {public int square(int x) {return x*x;}}public class SquareCalculatorTester{public static void main (String[] args) { ASquareCalculator squareCalculator = new ASquareCalculator();System.out.println (squareCalculator.square(5)); }}Calculates 5*5

#Changing Parameterpublic class ASquareCalculator {public int square(int x) {return x*x;}}public class SquareCalculatorTester{public static void main (String[] args) { ASquareCalculator squareCalculator = new ASquareCalculator();System.out.println (squareCalculator.square(341)); }}Must change code

#Rerun Programpublic class ASquareCalculator {public int square(int x) {return x*x;}}public class SquareCalculatorTester{public static void main (String[] args) { ASquareCalculator squareCalculator = new ASquareCalculator();System.out.println (squareCalculator.square(Ineteger.parseInt(args[0])); }}Must re-run programHow to not re-run program without writing tedious UI code?

#ObjectEditorpackage math; public class ASquareCalculator {public int square(int x) {return x*x;}}package main; import math.ASquareCalculator;import bus.uigen.ObjectEditor;public class SquareCalculatorTester{public static void main (String[] args) { ASquareCalculator squareCalculator = new ASquareCalculator();ObjectEditor.edit(squareCalculator ); }}ObjectEditor is predefined packaged class

#Editing ASquareCalculator Instance

#Invoking a Method And Viewing the Result

#Another Simple Class: ABMICalculatorASquareCalculatorABMICalculatorSpecification:Given an integer x, calculate the square of x.package math;public class ASquareCalculator {public int square(int x) {return x*x;}}Specification:Given the weight (kg) and height (m) of a person, calculate the persons body mass index a.k.a. BMI.?

#ABMICalculatorpackage bmi;public class ABMICalculator{public int calculateBMI(int weight, int height) {return weight/(height*height);}}Parameter and return types are integersBut height (m) and weight (kg) are expressed as decimalsHow do we solve the discrepancy?

#ABMICalculatorpackage bmi;public class ABMICalculator{public int calculateBMI(int weight, int height) {return weight/(height*height);}}doubleDoubles are decimal/real numbers

#ABMICalculatorpackage bmi;public class ABMICalculator{public double calculateBMI(double weight, double height) {return weight/(height*height);}}

#Formal vs. Actual Parameterspackage bmi;public class ABMICalculator{public double calculateBMI(double weight, double height) {return weight/(height*height);}}

weight0height0variablesmemoryParametersParametersInvoke calculateBMI Actual ParametersFormal Parameters74.981.94assigned

#Programmed Callpublic class ABMICalculator{public double calculateBMI(double weight, double height) {return weight/(height*height);}}public class BMICalculatorTester{ public static void main (String[] args) { ABMICalculator bmiCalculator = new ABMICalculator();System.out.println (bmiCalculator.calculateBMI(75, 1.77)); }}Formal ParametersActual Parameters

#Programmed vs. interactive callSystem.out.println(setWeight Called);Target ObjectMethod NameActual Parameters

Programmed CallInteractive Call

#Internal vs. External Method Callspublic class APoundInchBMICalculator {

public double calculateBMI( double weightInLbs, double heightInInches) {

return (new ABMICalculator()).calculateBMI( toKgs(weightInLbs), toMetres(heightInInches)); }

public double toMetres(double heightInInches) { } public double toKgs(double weightInLbs) { }}APoundInchBMICalculatorExternalCaller and callee methods are in different objectsMust specify target objectInternalCaller and callee methods are in the same objectTarget object is implicit (this)Actual parameters:

#Errorspackage bmi;class ABMICalculator{double calculateBMI(double weight, double height) {return (height*heigh)/weight}

Syntax ErrorLogic ErrorSemantics ErrorAccess Error

#Errorspackage bmi;class ABMICalculator{double calculateBMI(double weight, double height) {return (height*heigh)/weight}

Syntax ErrorLogic ErrorSemantics ErrorAccess Error

#Method Access Error

You instantiate a ABMICalculator objectbut there is no ABMICalculator menu itemReasonYou have not defined any public methods in ABMICalculator

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