An Enum (short for enumeration) is a custom data type that allows us to define a fixed set of named values. In other words, it specifies exactly which values a variable of that type can take. When defining an Enum, we list all possible values inside braces. This is similar to how built-in types like int have a defined range of allowed values, but in this case, we explicitly decide what those values are.

public enum Day {
    Mo, Tu, We, Th, Fr, Sa, Su
}                                                                         
                                    

public class Main {
    public static void main(String[] args) {
        System.out.println(Day.Tu); // works like using a predefined constant instead of a raw value

        Day number_of_a_day_of_the_week = Day.Mo;
        System.out.println(getDay(number_of_a_day_of_the_week));
    }

    private static String getDay(Day x) {
        return switch(x) {
            case Mo -> "Monday";
            case Tu -> "Tuesday";
            case We -> "Wednesday";
            case Th -> "Thursday";
            case Fr -> "Friday";
            case Sa -> "Saturday";
            case Su -> "Sunday";
        };
    }
}