Enum

1. What is an Enum?

An enum (short for enumeration) is a special Java type used to define a fixed set of named constant values, like the days of the week or the directions North, South, East, and West.

2. Why is it used?

When a value should only ever be one of a small, known set of options, an enum prevents invalid values from being used by mistake, unlike a plain String or int, which could accidentally hold anything.

3. Real-Life Example

Think of traffic light colours — only Red, Yellow, or Green are valid; there's no "Purple" traffic light. An enum locks a value down to only its officially defined options, just like a traffic light's fixed set of colours.

4. Syntax

java
enum EnumName {
    VALUE1, VALUE2, VALUE3
}

5. Example Program

java
enum Day {
    MONDAY, TUESDAY, WEDNESDAY
}

public class EnumDemo {
    public static void main(String[] args) {
        Day today = Day.TUESDAY;
        System.out.println("Today is: " + today);
    }
}

Output:

Today is: TUESDAY

6. Key Points to Remember

• Enum values are constants and are conventionally written in uppercase.
• An enum can also have fields, constructors, and methods, making it more powerful than a plain list of names.
• Using an enum instead of plain numbers or strings makes code safer and more readable.