Transcript Enumerated DATA Types

Enum Types
ENUMERATED DATA TYPES
Enumerated Data Types
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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
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Enumerated Types
 Known as an enum, it requires a declaration
and definition similar to a class
 Syntax:
List of all possible values
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; // entity of type Day named workDay
 Assignment of a value:
Day workDay = Day.WEDNESDAY;
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Enumerated Types
 Best practice is to define enumerated data
types in their own .java files
 For example:
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Enumerated Types
 An enum is a specialized class
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
address
Day.SUNDAY
Day.MONDAY
Day.TUESDAY
Day.WEDNESDAY
Day.THURSDAY
Day.FRIDAY
Day.SATURDAY
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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
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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
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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
Example
Day.java
Program output
EnumDemo.java
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Examples – values ( ) method
Face.java
For every Face f
in the set of all
values of Face
…
Called an
“enhanced for”
Output Results
Enumerated Data Types
Used to convert a String to its
corresponding enumerated
type’s value
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Enumerated Types - Switching
 One may use an enum constant with an if,
while, or switch
 See the example on next two slides
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Enum Example
This represents the entire
contents of the file named
Coin.java
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Enum example, continued
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Example
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Example, part 2
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