1. Enumerated DATA Types Enum Types Enumerated Data Types
February 18, 2019

2. What is an enumerated type?
Sometimes, a special data type is needed that has a small number of specific values
Day of the Week: Sunday, Monday, …
College Classification: Freshman, Sophomore, …
Political Party: Republican, Democrat, …
Sex: Female, Male
Suit: Clubs, Diamonds, Hearts, Spades
Coin: Penny, Nickel, Dime, Quarter, …
The Enumerated Data Type (enum) is designed for this purpose in Java
Enumerated Data Types
February 18, 2019

3. List of all possible values
Enumerated Types
Known as an enum, it requires a declaration and definition similar to a class
Syntax: enum typeName { one or more enum constants }
Definition example:
enum Day { SUNDAY, MONDAY, TUESDAY, WEDNESDAY,
THURSDAY, FRIDAY, SATURDAY }
Declaration of an instance of the Day type:
Day workDay; // ref to entity of type Day named workDay
Assignment of a value: Day workDay = Day.WEDNESDAY;
List of all possible values
Enumerated Data Types
February 18, 2019

4. Enumerated Types
Best practice is to define enumerated data types in their own .java files
For example:
Enumerated Data Types
February 18, 2019

5. Enumerated Types An enum is a specialized class address Day.SUNDAY
Each value is an object of type Day, a specialized enum class
Day workDay = Day.WEDNESDAY;
The workDay variable refers to (holds the address) of the Day.WEDNESDAY object
Day.SUNDAY
Day.MONDAY
Day.TUESDAY
address
Day.WEDNESDAY
Day.THURSDAY
Day.FRIDAY
Day.SATURDAY
Enumerated Data Types
February 18, 2019

6. Enumerated Types - Methods
toString – returns name of the constant
ordinal – returns the zero-based position of the constant in the enum. The values in the definition of the enum type are numbered beginning with 0. For example the ordinal for Day.THURSDAY is 4
equals – accepts an object as an argument and returns true if the argument is equal to the calling enum constant
compareTo - accepts an object as an argument and returns a negative integer if the calling constant’s ordinal < than the argument’s ordinal, a positive integer if the calling constant’s ordinal > than the argument’s ordinal, and zero if the calling constant’s ordinal == the argument’s ordinal
Enumerated Data Types
February 18, 2019

7. Enumerated Types: Methods, continued
values – requires no arguments but returns an array of all of the values the enumerated type has
valueOf – static method that returns the enumerated value corresponding to the string used as a parameter; an exception will be thrown if the string parameter does not exactly match one of the enumerated type’s values including the correct case
Enumerated Data Types
February 18, 2019

8. Converting Between String and Enum Type
Enum type String: use PhotoType.JPG.toString ( )
If you have an enum value and need a String, use the toString method of the enum type
String Enum: use PhotoType.valueOf (myStr)
If you have a String and need the equivalent enum value, use the valueOf method of the enum type
These methods are intended for conversions between valid enum values and the corresponding strings only

9. Example Day.java Program output EnumDemo.java Enumerated Data Types
February 18, 2019

10. Examples – values ( ) method
Face.java
For every Face f in the set of all values of Face …
Called an “enhanced for”
Output Results
Used to convert a String to its corresponding enumerated type’s value
Enumerated Data Types
February 18, 2019

11. Enumerated Types - Switching
One may use an enum constant with an if, while, or switch
See the example on next two slides
Enumerated Data Types
February 18, 2019

12. This represents the entire contents of the file named Coin.java
Enum Example
This represents the entire contents of the file named Coin.java
Enumerated Data Types
February 18, 2019

13. Enum example, continued
Enumerated Data Types
February 18, 2019