Enum

Enum

• An Enum is a special data type that represents a group of constants.
• Enums are used to define a fixed set of related constants, such as days of the week, directions, or states.
• Key characteristics:
  • Enums are implicitly final and static.
  • Enum constants are public, static, and final by default.
  • Enums can have fields, methods, and constructors.
  • Enums can implement interfaces but cannot extend classes (as they implicitly extend java.lang.Enum).

Basic ExampleWith Fields and MethodsWith Switch StatementImplementing an Interface

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

public class Main {
    public static void main(String[] args) {
        Day today = Day.MONDAY;
        System.out.println("Today is: " + today); // Outputs: Today is: MONDAY

        for (Day day : Day.values()) {
            System.out.println(day);
        }
    }
}

• Enums can have fields, methods, and constructors to associate additional data with each constant.

enum Planet {
    EARTH(5.97e+24, 6.371e6);

    private final double mass;   // in kilograms
    private final double radius; // in meters

    Planet(double mass, double radius) {
        this.mass = mass;
        this.radius = radius;
    }

    public double surfaceGravity() {
        final double G = 6.67430e-11; // Gravitational constant
        return G * mass / (radius * radius);
    }
}

public class Main {
    public static void main(String[] args) {
        System.out.println("Earth's Gravity: " + Planet.EARTH.surfaceGravity());
    }
}

• Enums are often used with switch statements for better readability and control.

enum TrafficLight {
    RED, YELLOW, GREEN
}

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

        switch (signal) {
            case RED -> System.out.println("Stop!");
            case YELLOW -> System.out.println("Get Ready!");
            case GREEN -> System.out.println("Go!");
        }
    }
}

• Enums can implement interfaces to define behavior for each constant.

interface Operation {
    double apply(double x, double y);
}

enum Calculator implements Operation {
    ADD {
        @Override
        public double apply(double x, double y) {
            return x + y;
        }
    },
    MULTIPLY {
        @Override
        public double apply(double x, double y) {
            return x * y;
        }
    };
}

public class Main {
    public static void main(String[] args) {
        System.out.println(Calculator.ADD.apply(10, 5)); // Outputs: 15.0
    }
}