// 使用 int 常量
public class Status {
    public static final int PENDING = 0;
    public static final int CONFIRMED = 1;
    public static final int SHIPPED = 2;
    // ...
}

// 使用 String 常量
public class RequestMethod {
    public static final String GET = "GET";
    public static final String POST = "POST";
    public static final String PUT = "PUT";
    // ...
}

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

public class EnumExample {
    public static void main(String[] args) {
        Day today = Day.MONDAY; // 聲明并賦值

        // 使用 switch 語(yǔ)句
        switch (today) {
            case MONDAY:
                System.out.println("It's Monday. Back to work!");
                break;
            case FRIDAY:
                System.out.println("It's Friday. Weekend is coming!");
                break;
            default:
                System.out.println("It's " + today.name() + ".");
                break;
        }

        // 比較枚舉實(shí)例（推薦使用 ==，因?yàn)樗鼈兪菃卫?
        if (today == Day.MONDAY) {
            System.out.println("Yes, it's Monday.");
        }

        // 使用 equals 方法（也可以，但 == 更高效）
        if (today.equals(Day.MONDAY)) {
            System.out.println("Yes, it's Monday (using equals).");
        }
    }
}

// 編譯器生成的類似代碼
final class Day extends Enum<Day> { // 枚舉類隱式繼承 Enum
    private static final Day SUNDAY = new Day("SUNDAY", 0);
    private static final Day MONDAY = new Day("MONDAY", 1);
    // ... 其他實(shí)例

    private static final Day[] $VALUES = {SUNDAY, MONDAY, /* ... */ SATURDAY};

    public static Day[] values() { // 自動(dòng)生成 values() 方法
        return $VALUES.clone();
    }

    public static Day valueOf(String name) { // 自動(dòng)生成 valueOf() 方法
        return Enum.valueOf(Day.class, name);
    }

    // 私有構(gòu)造函數(shù)，防止外部實(shí)例化
    private Day(String name, int ordinal) {
        super(name, ordinal);
    }
}

Day[] days = Day.values();
for (Day day : days) {
    System.out.println(day); // 輸出 SUNDAY, MONDAY, ...
}

Day day = Day.valueOf("MONDAY"); // 正確
// Day invalidDay = Day.valueOf("monday"); // 拋出 IllegalArgumentException，區(qū)分大小寫

System.out.println(Day.MONDAY.name()); // 輸出 "MONDAY"

System.out.println(Day.MONDAY.ordinal()); // 輸出 1
System.out.println(Day.SATURDAY.ordinal()); // 輸出 6

public enum OrderStatus {
    PENDING("待支付", false),
    CONFIRMED("已確認(rèn)", false),
    SHIPPED("已發(fā)貨", false),
    DELIVERED("已送達(dá)", true), // 最終狀態(tài)
    CANCELLED("已取消", true); // 最終狀態(tài)

    // 構(gòu)造函數(shù)是私有的，防止外部實(shí)例化
    private final String description;
    private final boolean isFinal;

    // 枚舉的構(gòu)造函數(shù)只能是 private 或 package-private
    OrderStatus(String description, boolean isFinal) {
        this.description = description;
        this.isFinal = isFinal;
    }

    // Getter 方法
    public String getDescription() {
        return description;
    }

    public boolean isFinal() {
        return isFinal;
    }

    // 可以添加自定義方法
    public boolean canTransitionTo(OrderStatus newStatus) {
        // 簡(jiǎn)單的邏輯：不能從最終狀態(tài)轉(zhuǎn)換到其他狀態(tài)
        if (this.isFinal) {
            return false;
        }
        // 這里可以定義更復(fù)雜的業(yè)務(wù)規(guī)則，例如 PENDING -> CONFIRMED -> SHIPPED -> DELIVERED
        // 為了演示，這里只檢查目標(biāo)狀態(tài)是否為最終狀態(tài)
        return true; // 簡(jiǎn)化邏輯
    }
}

// 使用示例
public class OrderStatusDemo {
    public static void main(String[] args) {
        OrderStatus status = OrderStatus.PENDING;

        System.out.println("Status: " + status.name());
        System.out.println("Description: " + status.getDescription());
        System.out.println("Is Final: " + status.isFinal());

        System.out.println("Can transition from PENDING to CONFIRMED? " + status.canTransitionTo(OrderStatus.CONFIRMED));
        System.out.println("Can transition from DELIVERED to CANCELLED? " + OrderStatus.DELIVERED.canTransitionTo(OrderStatus.CANCELLED));
    }
}

public enum HttpMethod {
    GET("Retrieves information from the server"),
    POST("Submits data to be processed to the server"),
    PUT("Updates an existing resource on the server"),
    DELETE("Deletes a specified resource from the server");

    private final String meaning;

    HttpMethod(String meaning) {
        this.meaning = meaning;
    }

    public String getMeaning() {
        return meaning;
    }

    // 可以重寫 toString 方法，提供更有意義的字符串表示
    @Override
    public String toString() {
        return name() + ": " + meaning;
    }
}

// 使用示例
HttpMethod method = HttpMethod.POST;
System.out.println(method); // 輸出 "POST: Submits data to be processed to the server"

public enum Operation {
    PLUS {
        @Override
        public double apply(double x, double y) {
            return x + y;
        }
    },
    MINUS {
        @Override
        public double apply(double x, double y) {
            return x - y;
        }
    },
    TIMES {
        @Override
        public double apply(double x, double y) {
            return x * y;
        }
    },
    DIVIDE {
        @Override
        public double apply(double x, double y) {
            if (y == 0) throw new ArithmeticException("Cannot divide by zero");
            return x / y;
        }
    };

    // 定義抽象方法
    public abstract double apply(double x, double y);
}

// 使用示例
public class Calculator {
    public static void main(String[] args) {
        Operation op = Operation.PLUS;
        double result = op.apply(4.0, 5.0);
        System.out.println(result); // 輸出 9.0

        op = Operation.DIVIDE;
        result = op.apply(10.0, 2.0);
        System.out.println(result); // 輸出 5.0
    }
}

interface Named {
    String getName();
}

interface Describable {
    String getDescription();
}

public enum Planet implements Named, Describable {
    MERCURY("Mercury", "The smallest planet"),
    VENUS("Venus", "The hottest planet"),
    EARTH("Earth", "Our home planet");

    private final String name;
    private final String description;

    Planet(String name, String description) {
        this.name = name;
        this.description = description;
    }

    @Override
    public String getName() {
        return name;
    }

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

try {
    OrderStatus status = OrderStatus.valueOf(inputStatusString.toUpperCase());
    // ...
} catch (IllegalArgumentException e) {
    System.err.println("Invalid status: " + inputStatusString);
    // 處理無(wú)效輸入
}