Java Enums: Enumeration and Implementation

• Enums are enumeration classes used to represent a fixed set of named constants.

Enumeration

• Enumeration involves listing all values for a defined set, useful in programming for working with well-defined value sets.
• Examples of enumerations: days of the week (Sunday, Monday, Tuesday...), months (January, February, ...), planets (Mercury, Venus...), card suits (Hearts, Diamonds, Spades, Clubs), door states (Open, Closed), directions (North, East, South, West), and grades (A+, A, A-, B+, B...).

Enums in Java

• Java provides an enum type to specify a list of items.
• Enums are similar to classes but have a defined, finite set of objects.
• Using constant integers is an older, less reliable approach that has been deprecated.
• Enumerated data types consist of predefined values and create variables holding only the values within the enumerated data type

Creating Enums

• BlueJ simplifies enum creation; start with a basic day enum then modify it.
• Enum values are typically written in UPPERCASE_WITH_UNDERSCORES, following constant naming standards.
• The basic Day enum results in 7 objects, such as MONDAY:Day, TUESDAY:Day, etc.

Enum Methods

• The values() method returns an array containing all enum values.
• For a Day enum, the values() method generates an array, like {Day.MONDAY, Day.TUESDAY, ..., Day.SUNDAY}.
• Enums have a defined toString() method that returns the name of the enum.

Comparing Enum Values

• Enum instances have only one copy; compare them using == instead of .equals().
• All variables pointing to the same enum value (e.g., Day.SATURDAY) share the same address.
• The valueOf() method takes a string and returns the enum instance with the matching name.
• Day friday = Day.valueOf("FRIDAY") would return Day.FRIDAY.
• valueOf() is case-sensitive hence, Day today = Day.valueOf(userDay.toUpperCase());

Enum Objects

• Enums can be more complex, holding methods and other values
• Enhanced Day enum can determine if the day is a weekend
• Values for the constructor included when listing the instances

EnhancedDay Enum

• You can also declare the field and create a constructor
• You must declare the field as well as the constructor that take in the proper parameters
• Methods will be required for each field (typically a getter)

EnhancedDay Example

• A complex enum will simplify code that uses the enum.
• See CalculatePayForEnhancedDay.java

Enum Summary

• Enums cannot be instantiated with new.
• If enums have fields: provide values in parentheses, these values are passed to the private constructor, and the JVM calls the constructor automatically.
• Enums can include methods for setting or getting values.

Explore Java enums for representing fixed sets of named constants. Learn about enumeration concepts, creating enums in Java, and their usage in programming. Enums provide a type-safe way to define a list of items, offering a more reliable alternative to constant integers.