Declaring enums

Learn constant sets with enum.

Enum: a named set of constants

An enum represents a fixed set of values. It is used for limited options like days of the week, seasons or directions. Each constant is written in uppercase.

enum Day {
  MONDAY, TUESDAY, WEDNESDAY,
  THURSDAY, FRIDAY, SATURDAY, SUNDAY
}

An enum is really a special kind of class; its constants are automatically public static final. To assign a constant to a variable you write Day d = Day.MONDAY;. This way typos are caught at compile time, which is safer than using strings.

ordinal and name

Every enum constant has an ordinal number (ordinal()) and a name (name()). The ordinal starts at zero and increases in declaration order.

Day d = Day.WEDNESDAY;
System.out.println(d.ordinal()); // 2
System.out.println(d.name());    // WEDNESDAY

ordinal() is rarely needed; relying on the number is riskier than using the constant itself. name() returns the string form of the constant, which is useful for logging.

Exercise Define a color enum and print it

Define a Color enum with constants RED, GREEN, BLUE. Assign the RED constant to a variable and print it.

Show example solution

enum Color { RED, GREEN, BLUE }
// inside main:
Color c = Color.RED;
System.out.println(c);

Test yourself

Match each enum constant to its description

MONDAY

First day of week
SUNDAY

Last day of week
WEDNESDAY

Middle day
FRIDAY

Friday
Assign an enum constant
```
Day d = Day.____;
```
Show answer
```
Day d = Day.MONDAY;
```
Which of the following is a valid enum declaration?
- enum Color = RED, GREEN, BLUE;
- enum Color { RED, GREEN, BLUE }
- enum Color { red, green, blue }
- Color enum { RED, GREEN, BLUE }
Show answer

enum Color = RED, GREEN, BLUE; — enum constants are uppercase and separated by commas inside braces.

Next lesson: values and valueOf

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