Java Enum

In Java an enumerated type is a type that specifies a sequence of named constants. Not to mention that theses constants are related. The days of week or months of year can be good examples of enums. Prior to Java 5 Java developers had to use sets of named integer constants to simulate enum type behavior. Starting with Java 5 the developers got the built-in support of enums in Java.

An enum in Java is an enumerated type that is declared with the reserved key word enum. Consider the following piece of code:

enum DaysOfWeek {

FRIDAY,

SATURDAY,

SUNDAY,

MONDAY,

TUESDAY,

WEDNESDAY,

THURSDAY

}

It is a convention to write enum members in Capital Letters. Please note that unlike enumerated types in other languages like C++ and C#, enums in Java are not integer based. They are pure classes. Each member of the enum is a public static final field, representing an instance of its enum class.

Enum ensure compile-time type safety by preventing a developer from assigning illegal values to an enum type. Consider the following piece of code:

enum DaysOfWeek {

FRIDAY,

SATURDAY,

SUNDAY,

MONDAY,

TUESDAY,

WEDNESDAY,

THURSDAY

}

enum Fruits {

MANGO,

ORANGE,

APPLE,

BANANA,

APRICOT,

PINEAPPLE

}

DaysOfWeek today = Fruits.MANGO; //compile-time error

The above code would signal errors at compile time. Please note that if the enums were int-based in Java the above could would have compiled successfully. The fact that they are pure Java objects, prevented the above code from compiling successfully.

 

The enums in Java, like other objects, provide a toString() method that returns a meaningful description of a constant’s value.