อีนัมที่มีฟิลด์และเมธอด

ชนิดแจกแจงเป็นคลาสที่สมบูรณ์

public class Main {
    enum Direction { NORTH, SOUTH, EAST, WEST }
    public static void main(String[] args) {
        Direction d = Direction.NORTH;
        System.out.println(d + " is a " + d.getClass().getSuperclass().getSimpleName());
    }
}

การเพิ่มฟิลด์

public class Main {
    enum Planet {
        EARTH(9.81), MARS(3.71), JUPITER(24.79);
        private final double gravity;
        Planet(double gravity) { this.gravity = gravity; }
        double gravity() { return gravity; }
    }
    public static void main(String[] args) {
        System.out.println("Mars gravity: " + Planet.MARS.gravity());
    }
}

ตัวสร้างของชนิดแจกแจงเป็นแบบส่วนตัว

public class Main {
    enum Coin {
        PENNY(1), NICKEL(5), DIME(10), QUARTER(25);
        private final int cents;
        Coin(int cents) { this.cents = cents; }
        int cents() { return cents; }
    }
    public static void main(String[] args) {
        int total = Coin.QUARTER.cents() + Coin.DIME.cents();
        System.out.println("Total cents: " + total);
    }
}

หลายฟิลด์

public class Main {
    enum Planet {
        EARTH(5.976e24, 6.37814e6),
        MARS(6.421e23, 3.3972e6);
        private final double mass, radius;
        Planet(double mass, double radius) { this.mass = mass; this.radius = radius; }
        double surfaceGravity() {
            final double G = 6.67300E-11;
            return G * mass / (radius * radius);
        }
    }
    public static void main(String[] args) {
        System.out.printf("Earth g = %.2f%n", Planet.EARTH.surfaceGravity());
    }
}

เมธอดของอินสแตนซ์

public class Main {
    enum Size {
        SMALL(8), MEDIUM(12), LARGE(16);
        private final int ounces;
        Size(int ounces) { this.ounces = ounces; }
        int ounces() { return ounces; }
        double liters() { return ounces * 0.0295735; }
    }
    public static void main(String[] args) {
        System.out.printf("Large = %.2f L%n", Size.LARGE.liters());
    }
}

ชื่อที่มีมาในตัวและลำดับ

public class Main {
    enum Day { MON, TUE, WED }
    public static void main(String[] args) {
        for (Day d : Day.values()) {
            System.out.println(d.name() + " -> ordinal " + d.ordinal());
        }
    }
}

values และ valueOf

public class Main {
    enum Status { ACTIVE, PAUSED, CLOSED }
    public static void main(String[] args) {
        System.out.println("count: " + Status.values().length);
        Status s = Status.valueOf("PAUSED");
        System.out.println("parsed: " + s);
    }
}

การเขียนทับ toString

public class Main {
    enum Priority {
        LOW, MEDIUM, HIGH;
        @Override public String toString() {
            return name().charAt(0) + name().substring(1).toLowerCase();
        }
    }
    public static void main(String[] args) {
        for (Priority p : Priority.values()) System.out.println(p);
    }
}

อีนัมในคำสั่งสวิตช์

public class Main {
    enum Traffic { RED, YELLOW, GREEN }
    static String action(Traffic t) {
        return switch (t) {
            case RED -> "Stop";
            case YELLOW -> "Slow down";
            case GREEN -> "Go";
        };
    }
    public static void main(String[] args) {
        System.out.println(action(Traffic.GREEN));
    }
}

แมปการค้นหาแบบคงที่

import java.util.HashMap;
import java.util.Map;

public class Main {
    enum Op {
        PLUS("+"), MINUS("-");
        private final String symbol;
        Op(String symbol) { this.symbol = symbol; }
        private static final Map<String, Op> BY_SYMBOL = new HashMap<>();
        static { for (Op o : values()) BY_SYMBOL.put(o.symbol, o); }
        static Op fromSymbol(String s) { return BY_SYMBOL.get(s); }
    }
    public static void main(String[] args) {
        System.out.println(Op.fromSymbol("-"));
    }
}

อีนัมใช้อินเทอร์เฟซ

public class Main {
    interface Describable { String describe(); }
    enum Animal implements Describable {
        DOG, CAT;
        public String describe() { return "A " + name().toLowerCase(); }
    }
    public static void main(String[] args) {
        Describable d = Animal.DOG;
        System.out.println(d.describe());
    }
}

ตรวจสอบความเข้าใจ

ทบทวน

public class Main {
    enum Greeting { HELLO; String text() { return "Hi"; } }
    public static void main(String[] args) {
        System.out.println("Enum fields recap: " + Greeting.HELLO.text());
    }
}