Java enum
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This document discusses Java enums, which define a fixed set of constants. Enums can have fields and methods like classes. They are useful any time a set of fixed constants is needed, such as for months, directions, or colors. Enums implicitly extend Enum and cannot extend anything else. They provide type safety and can be used in collections without boxing/unboxing. The document also describes EnumSet and EnumMap as high performance implementations for enums.
Java enum
- 1. Java Enum Sujit Kumar Zenolocity LLC Copyright @ 2012 - 2024
- 2. Enums • An enum type is a type whose fields consist of a fixed set of constants. • The names of an enum type's fields are in uppercase letters. • Example: public enum Day { SUNDAY, MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY, SATURDAY }
- 3. When to use Enums • Use an Enum any time you need to represent a fixed set of constants. • Examples: Months of Year Days of Week Entries in a Menu Colors Directions of Compass
- 4. Enums (contd…) • Enums are like classes, they can have fields (state) and methods (behavior). • All enums implicitly extend java.lang.Enum. Since Java does not support multiple inheritance, an enum cannot extend anything else. • Typesafe => compile-time error checking. • You can use a switch on enum values.
- 5. Enums (contd…) • toString() returns the enum value as a String — can be overridden. • values() method returns an array of all the enum values. • Can be used in collections as objects more efficiently than int values — no boxing/unboxing required! • Implement the Comparable and Serializable interfaces.
- 6. High Performance Set and Map implementations for Enums • EnumSet All of the members of an EnumSet must be of the same enum type. Supports iteration over a range of enum types. • EnumMap Almost the same speed as an array. If you want to map an enum to a value, use an EnumMap instead of an array. EnumMap's implementation uses an array and for that reason has slightly better performance than HashMaps.