Slide 1Program Components ~ Physical ObjectsProgram Objects ~ Manufactured ObjectsClassification Through FactoriesClassification Through ClassesA Simple Instantiated ClassPackagesPackagesPackagesPackagesPackagesLong name with no importWhy imports/full name?Ambiguous ImportWhy Packages?Browsing Java ClassesLanguage vs. LibraryChanging ParameterChanging ParameterRerun ProgramObjectEditorEditing ASquareCalculator InstanceInvoking a Method And Viewing the ResultAnother Simple Class: ABMICalculatorABMICalculatorABMICalculatorABMICalculatorFormal vs. Actual ParametersProgrammed CallProgrammed vs. interactive callInternal vs. External Method CallsErrorsMethod Access ErrorExtra slidesProgram Objects ~ Manufactured ObjectsProgram Objects ~ Manufactured ObjectsCOMP 401OBJECTSInstructor: Prasun Dewan2PROGRAM COMPONENTS ~ PHYSICAL OBJECTSNatural ObjectsManufactured Objects~ Program Components~ Program Components3PROGRAM OBJECTS ~ MANUFACTURED OBJECTS manufactured byperform OperationsaccelerateacceleratebrakebrakeClassProgram ObjectProgram ObjectProgram ObjectProgram Objectinstance ofMethodsaddaddsubtractsubtractexecute invoke callFactoryInvoking new operation on class ~ ordering new car from factory4CLASSIFICATION THROUGH FACTORIESmanufacturedbymanufacturedby5CLASSIFICATION THROUGH CLASSESASquareCalculatorABMICalculatorASquareCalculator InstanceASquareCalculator InstanceASquareCalculator InstanceASquareCalculator InstanceABMICalculator InstanceABMICalculator InstanceABMICalculator InstanceABMICalculator Instanceinstance ofinstance of6A 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 CreationObject UseObject UseNo static because class will be instantiatedNo static because class will be instantiatedNo packageNo package7PACKAGESpackage 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)Class in different package must be imported using full name of class ( a la full file name)8PACKAGESpackage 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 importedClass in same package need not be imported9PACKAGESpackage 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 neededNo package means package named default, hence import needed10PACKAGESpublic 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 hereNo package means package named default, hence no import needed here11PACKAGESpublic 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 nameShort name of class in default package same as its full name12LONG 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) { math.ASquareCalculator squareCalculator = new math.ASquareCalculator();System.out.println (squareCalculator.square(5)); }}Can use the full name of class directlyCan use the full name of class directly13package 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 intsTwice the size of intsDisambiguatesDisambiguates14package safemath; public class ASquareCalculator {public long square(int x) {return x*x;}}AMBIGUOUS 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)); }}AmbiguousAmbiguous15WHY PACKAGES?Can create competing implementations of same class.A la creating files Test.java in different assignment directories/foldersCan browse related classesA la browsing through all files in an assignment directory/folder.Like directories/folders packages can be hierarchicalpackage math.power;public class ACubeCalculator {…}16BROWSING JAVA CLASSESVery useful packageVery useful package17LANGUAGE VS. LIBRARYBuilt-in classesBuilt-in classesDo not have to be explicitly importedDo not have to be explicitly imported18CHANGING 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*5Calculates 5*519CHANGING PARAMETERpublic class ASquareCalculator {public int square(int x) {return x*x;}}public class