Building Java ProgramsChapter outlineClasses, types, and objectsObjects and "OOP"AbstractionFactory/blueprint analogyRecall: Point objectsRecall: Point data/methodsA Point classObject state: fieldsPoint class, version 1FieldsAccessing fieldsClient codeClient code questionObject behavior: instance methodsClient code redundancyEliminating redundancy, v1Classes with behaviorInstance methodsPoint object diagramsThe implicit parameterTracing instance method callsPoint class, version 2Instance method questionsAccessors and mutatorsClient code, version 2Slide 28Object initialization: constructorsInitializing objectsConstructorsPoint class, version 3Tracing constructor callsClient code, version 3Slide 35EncapsulationSlide 37Implementing encapsulationEncapsulation and accessorsBenefits of encapsulationPoint class, version 4Preconditions, postconditions, and invariantsPre/postconditionsClass invariantsViolated preconditionsDealing with violationsThrowing exceptions exampleEncapsulation and invariantsSpecial instance methods: toString, equalsProblem: object printabilityThe toString methodtoString method syntaxRecall: comparing objectsThe equals methodInitial flawed equals methodequals and the Object classAnother flawed versionType-casting objectsCasting objects diagramComparing different typesThe instanceof keywordFinal version of equals methodThe keyword thisUsing the keyword thisVariable shadowingAvoiding shadowing with thisMultiple constructorsMultiple constructors w/ thisMore class problemsObject practice problemSlide 71Slide 72Calculator client codeCopyright 2006 by Pearson Education1Building Java Building Java ProgramsProgramsChapter 8: ClassesCopyright 2006 by Pearson Education2Chapter outlineobjects, classes, and object-oriented programmingrelationship between classes and objectsabstractionanatomy of a classfieldsinstance methodsconstructorsencapsulationadvanced classespreconditions, postconditions, and invariantsspecial methods: toString and equalsthe keyword thisCopyright 2006 by Pearson Education3Classes, types, and objectsclass:1. A module that can be run as a program.2. A template for a type of objects.We can write Java classes that are not programs in themselves, but instead define new types of objects.We can use these objects in our programs if we so desire.Why would we want to do this?Copyright 2006 by Pearson Education4Objects and "OOP"object: An encapsulation of data and behavior.object-oriented programming (OOP): Writing programs that perform most of their useful behavior through interactions with objects.So far, we have interacted with objects such as:StringPointScannerDrawingPanelGraphicsColorRandomFilePrintStreamCopyright 2006 by Pearson Education5Abstractionabstraction: A distancing between ideas and details.The objects in Java provide a level of abstraction, because we can use them without knowing how they work.You use abstraction every day when interacting with technological objects such as a portable music player.You understand its external behavior (buttons, screen, etc.)You DON'T understand its inner workings, nor do you need to.Copyright 2006 by Pearson Education6Factory/blueprint analogyIn real life, a factory can create many similar objects.This is also like following a blueprint.Music player factorystate: # of players madebehavior: directions on how to build a music playerMusic player #1state: station/song, volume, battery lifebehavior: power on/of change station/song change volume choose random songMusic player #2state: station/song, volume, battery lifebehavior: power on/of change station/song change volume choose random songMusic player #3state: station/song, volume, battery lifebehavior: power on/of change station/song change volume choose random songcreatesCopyright 2006 by Pearson Education7Recall: Point objectsJava has a class of objects named Point.To use Point, you must write: import java.awt.*;Constructing a Point object, general syntax:Point <name> = new Point(<x>, <y>);Point <name> = new Point(); // the origin, (0, 0)Examples:Point p1 = new Point(5, -2);Point p2 = new Point();Point objects are useful for several reasons:They store two values, an (x, y) pair, in a single variable.They have useful methods we can call in our programs.Copyright 2006 by Pearson Education8Recall: Point data/methodsData stored in each Point object:Useful methods of each Point object:Point objects can also be printed using println statements:Point p = new Point(5, -2);System.out.println(p); // java.awt.Point[x=5,y=-2]Method name Descriptiondistance(p) how far away the point is from point psetLocation(x, y) sets the point's x and y to the given valuestranslate(dx, dy) adjusts the point's x and y by the given amountsField name Descriptionxthe point's x-coordinateythe point's y-coordinateCopyright 2006 by Pearson Education9A Point classA Point class might look something like this:Each object contains its own data and methods.The class has the instructions for how to construct individual objects.Point classpublic Point()public Point(int x, int y)Point object #1state: int x, ybehavior: distance(Point p) equals(Point p) setLocation(int x, int y) toString() translate(int dx, int dy)Point object #2state: int x, ybehavior: distance(Point p) equals(Point p) setLocation(int x, int y) toString() translate(int dx, int dy)Point object #3state: int x, ybehavior: distance(Point p) equals(Point p) setLocation(int x, int y) toString() translate(int dx, int dy)allowsconstruction ofCopyright 2006 by Pearson Education10Object state:Object state:fieldsfieldsreading: 8.2Copyright 2006 by Pearson Education11Point class, version 1The following code creates a new class named Point.public class Point { int x; int y;}We'd save this code into a file named Point.java.Each object contains two pieces of data:an int named x,an int named y.Point objects (so far) do not contain any behavior.Copyright 2006 by Pearson Education12Fieldsfield: A variable inside an object that represents part of the internal state of the object.Each object will have its own copy of the data fields we declare.Declaring a field, general syntax:<type> <name> ;Examples:public class Student { String name; // each student object has a double gpa; // name and gpa data field}Copyright 2006 by Pearson