Question of the Day You overhear a boy & his mother talking: Mom:What is ? Boy: That's easy, 33. Mom: Good. What's ? Boy:Simple. It's 40. Mom:Excellent! Now what's ? Boy: Boring. The answer is 37. Mom:Perfect! Once you see how the boy is dressed it all makes sense. What is the boy wearing?

Question of the Day You overhear a boy & his mother talking: Mom:What is ? Boy: That's easy, 33. Mom: Good. What's ? Boy:Simple. It's 40. Mom:Excellent! Now what's ? Boy: Boring. The answer is 37. Mom:Perfect! Once you see how the boy is dressed it all makes sense. What is the boy wearing? A football uniform

Announcements  If you need more review of Java…  I have lots of good resources – talk to me  Use “Additional Help” link on webpage  Weekly assignments problems due before class  Remove rust from summer and get back into coding  Problems designed to help learn new material, too

Data Types  8+1 primitive data types  Examples: boolean, byte, char, int, double, String *  Only types that work with Java operators  Operators include: +, -, %, &&, ||, >=, <, !  Primitives used natively by computers  Means that using them is very quick  Implies greater support within the language

Primitive Types  Primitive variables are simple to use  Each variable is a “xerox” holding a value  Assignment copies value  Update variable being assigned only

Java Enumerations

Enumeration Methods  enum instances always include these methods  public String name() Returns String equal to actual instances' name  public int ordinal() Position in listing where instance was declared  Can also find all enumerated instances  public static EnumName[] values() Returns array of values enumerated by EnumName

Java Enumerations  Must be written in file EnumName.java public enum EnumName { Instance0, Instance1, Instance2; }  Can be used in methods elsewhere: EnumName var = EnumName.Instance0; System.err.println(var.name()); if (var.ordinal() > 1) { System.err.println(“Got Instance2!”); } EnumName[] arr = EnumName.values();

Quick Quiz  Should you be taking notes? Let’s see… 1. What are the 3 methods defined by each enum ? 2. What do each of these methods do? 3. Can you use ever compare an enum using “ > ”?

Classes  Real world needs more than primitives  Additional types defined by classes in Java  Classes usually begin with: public class ClassNameGoesHere {  By convention, name starts with capital letter  Use interior capitals to highlight words in name  Should be in file named ClassNameGoesHere.java  ClassNameGoesHere becomes type to use

Creating Instances  Use instances of a class  Keyword new creates instances: public class Kitty {... } new Kitty(...);

Reference Variables  Variables of class type are references  Must assign variable to instance before use  Variable is null when not referring to any instance  Work similar to a remote control  Reference is not object, but refers to object TV telly = new TV(...);

Reference Variables  Variables of class type are references  Must assign variable to instance before use  Variable is null when not referring to any instance  Work similar to a remote control  Reference is not object, but refers to object TV telly = new TV(...); telly

Reference Variables  Variables of class type are references  Must assign variable to instance before use  Variable is null when not referring to any instance  Work similar to a remote control  Reference is not object, but refers to object TV telly = new TV(...); telly

Reference Variables  Variables of class type are references  Must assign variable to instance before use  Variable is null when not referring to any instance  Work similar to a remote control  Reference is not object, but refers to object TV telly = new TV(...); telly

Using Instances  Use instances of a class  Each instance is unique  Each instance is unique Kitty cat = new Kitty(...); cat

Using Instances  Use instances of a class  Each instance is unique  Each instance is unique Kitty cat = new Kitty(...); Kitty tiger = new Kitty(...); cattiger

Using Instances  Use instances of a class  Each instance is unique  Each instance is unique Kitty cat = new Kitty(...); Kitty tiger = new Kitty(...); cat = new Kitty(...); cattiger

Using Instances  Use instances of a class  Each instance is unique  Each instance is unique Kitty cat = new Kitty(...); Kitty tiger = new Kitty(...); cat = new Kitty(...); cattiger

Using Instances  Use instances of a class  Each instance is unique  Each instance is unique Kitty cat = new Kitty(...); Kitty tiger = new Kitty(...); cat = new Kitty(...); cattiger

Working With References  Assignments alias references  Only way to create instance using new  Refer to same instance when aliased

Working With References  Assignments alias references  Only way to create instance using new  Refer to same instance when aliased Kitty cat, tiger; cat tiger

Working With References  Assignments alias references  Only way to create instance using new  Refer to same instance when aliased Kitty cat, tiger; cat = new Kitty(...); cat tiger

Working With References  Assignments alias references  Only way to create instance using new  Refer to same instance when aliased Kitty cat, tiger; cat = new Kitty(...); tiger = new Kitty(...); cat tiger

Working With References  Assignments alias references  Only way to create instance using new  Refer to same instance when aliased Kitty cat, tiger; cat = new Kitty(...); tiger = new Kitty(...); tiger = cat; cat tiger

 Aliased variables refer to same instance  Single instance get changes to aliased variables  Aliased variables see all changes that are made  But, assignments only affect the one variable Kitty cat, tiger, kat; cat = new Kitty(...); tiger = new Kitty(...); kat = tiger; tiger = cat; cat = kat; tiger = null; Aliasing cat tiger kat

Your Turn  Get into your groups and complete activity

For Next Lecture  Reading from AF Chapters 8 & 9 for Wednesday  What is the advantages of using arrays?  When & why can it suck to use arrays?  Are arrays like primitives or references?  There is weekly assignment problem on Angel  Due before Wednesday’s lecture (via )  Get back into the swing of writing Java code