Question of the Day  What card(s) must you flip to verify the following statement: Cards with a vowel on one side, have an even number on the other side. A A B B

Question of the Day  What card(s) must you flip to verify the following statement: Cards with a vowel on one side, have an even number on the other side. A A B B

Announcements  If you need more review of Java…  I have lots of good resources – talk to me  Use “Additional Help” link on webpage

Classes vs. Objects  Classes are blueprints describing data type  On their own, classes (usually) cannot do anything  Objects are instances of a class  New objects created (instantiated) using new  Fields describe state of an object  Object’s behavior represented by methods

Instance Variables  All of class's instances have same fields…  … but values can differ between each instance  In a class, each field must have unique name  Different classes can duplicate names of fields  Field declaration must include data type  Will act like variables of that type  Can be primitive, enum, or reference type

Class Example public class Car { /** What kind of car & who made it */ private String makeAndModel; /** Color of the car. */ private String color; /** Percent full the gas tank is */ private float tankLevel; /** Miles recorded on the odometer */ private int odometerReading; /* Definition continues from here */

Using Fields (1) Car profHertzCar = new Car(); profHertzCar.makeAndModel = “BMW Z4”; profHertzCar.color = “Deep Green Metallic”; profHertzCar.tankLevel = 1.0; profHertzCar.odometerReading = 10000; Car actualCar = new Car(); actualCar.makeAndModel = “Subaru Outback"; actualCar.color = “Brown”; actualCar.tankLevel = ; actualCar.odometerReading = 67634;

Using Fields (2) Car dreamCar = new Car(); dreamCar.makeAndModel = “BMW Z4”; dreamCar.color = “Deep Green Metallic”; dreamCar.tankLevel = 1.0; dreamCar.odometerReading = 10000;

Using Fields (2) Car dreamCar = new Car(); dreamCar.makeAndModel = “BMW Z4”; dreamCar.color = “Deep Green Metallic”; dreamCar.tankLevel = 1.0; dreamCar.odometerReading = 10000; Car realCar = dreamCar; realCar.makeAndModel = “Subaru Outback”; realCar.color = “Silver”; realCar.tankLevel = ; realCar.odometerReading = 67634;

Using Fields (2) Car dreamCar = new Car(); dreamCar.makeAndModel = “BMW Z4”; dreamCar.color = “Deep Green Metallic”; dreamCar.tankLevel = 1.0; dreamCar.odometerReading = 10000; Car realCar = dreamCar; realCar.makeAndModel = “Subaru Outback”; realCar.color = “Silver”; realCar.tankLevel = ; realCar.odometerReading = 67634;

static Fields  Some data belongs to class, not instance Float.MAX_VALUE Citizen.nationalPopulation Instructor.bestProfessor  static fields used for any class-based data  All of the class’s instances see same value  Do not need an instance to access this value  Can be updated via any instance or via class

static Code Use Example public class Player { public static int num; public String name; public static void main(String[] args) { Player player1, player2, player3; player1 = new Player(); player1.name = "Homer"; player1.num += 1; player2 = new Player(); player2.name = “JJ"; Player.num += 1; player3 = player2; player3.name = "Hertz"; System.out.print(player2.name+" "+player1.num); } }

Tracing With Objects & Fields public static void main(String[] args) { Player player1, player2, player3; player1 = new Player(); player1.name = "Homer"; player1.num += 1; player2 = new Player(); player2.name = “JJ"; Player.num += 1; player3 = player2; player3.name = "Hertz"; System.out.print(player2.name+" "+player1.num); }

static v. non- static Review static fieldsnon- static fields  Belong to class as a whole  No instance needed to use  Can set value at any time  No limit on use in code  Primitive or reference okay static  Declare in class using: static type name;  Values are instance-based  Must specify instance to use  Can set value at any time  No limit on use in code  Primitive or reference okay  Declare in class using: type name;

Your Turn  Get into your groups and complete activity

For Next Lecture  Keep reviewing your Java lessons  Will be discussing methods & constructors Friday  Really need to be back up-to-speed at that point  There is weekly assignment problem on Angel  Due next Tuesday at 5PM but could start earlier  With this finish removing rust from lazy summer