Java.Core.What is the enum type in Java? Provide examples of its use.

In Java, an enum (short for “enumeration”) is a special data type used to define a collection of constants. Each constant in an enum is implicitly public, static, and final. Enums are commonly used when a variable can take only a limited set of values, such as days of the week, directions, or states in a finite state machine.

Basic Example

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

public class EnumExample {
    public static void main(String[] args) {
        Day today = Day.FRIDAY;

        if (today == Day.FRIDAY) {
            System.out.println("It's almost the weekend!");
        }

        // Loop through all enum values
        for (Day d : Day.values()) {
            System.out.println(d);
        }
    }
}

Output:

It's almost the weekend!
SUNDAY
MONDAY
TUESDAY
WEDNESDAY
THURSDAY
FRIDAY
SATURDAY

Enum with Fields, Constructor, and Methods

Enums can have attributes, constructors, and methods.

enum Size {
    SMALL("S"), MEDIUM("M"), LARGE("L"), EXTRALARGE("XL");

    private String abbreviation;

    // Constructor
    Size(String abbreviation) {
        this.abbreviation = abbreviation;
    }

    public String getAbbreviation() {
        return abbreviation;
    }
}

public class EnumWithFields {
    public static void main(String[] args) {
        Size size = Size.MEDIUM;
        System.out.println("Size: " + size);
        System.out.println("Abbreviation: " + size.getAbbreviation());
    }
}

Output:

Size: MEDIUM
Abbreviation: M

Enum in Switch Statement

Enums work well with switch statements.

public class EnumSwitchExample {
    enum TrafficLight {
        RED, YELLOW, GREEN
    }

    public static void main(String[] args) {
        TrafficLight signal = TrafficLight.RED;

        switch (signal) {
            case RED:
                System.out.println("Stop!");
                break;
            case YELLOW:
                System.out.println("Get ready...");
                break;
            case GREEN:
                System.out.println("Go!");
                break;
        }
    }
}

Output:

Stop!

Enum Implementing an Interface

Enums can implement interfaces.

interface Describable {
    String getDescription();
}

enum Status implements Describable {
    SUCCESS("Operation successful"),
    ERROR("Operation failed"),
    PENDING("Operation pending");

    private String description;

    Status(String description) {
        this.description = description;
    }

    @Override
    public String getDescription() {
        return description;
    }
}

public class EnumInterfaceExample {
    public static void main(String[] args) {
        Status s = Status.SUCCESS;
        System.out.println(s + ": " + s.getDescription());
    }
}

Output:

SUCCESS: Operation successful

Key Features of Enums in Java

• Type-safe and prevent invalid values.
• Can have fields, methods, and constructors.
• Can implement interfaces but cannot extend classes.
• Can be used in switch statements.
• The values() method returns all possible values of an enum.

Enums are widely used in Java for defining fixed sets of constants, making code more readable and maintainable.