Java枚举键值存储技巧

• EnumMap不能包含null键，但可以有null值
• 所有键必须来自同一个枚举类型
• Map的遍历顺序与枚举常量的定义顺序一致

enum OrderStatus {
    PENDING,
    SHIPPED,
    DELIVERED,
    CANCELLED
}

public class OrderProcessor {
    private static final EnumMap<OrderStatus, String> statusMessages =
        new EnumMap<>(OrderStatus.class);

    static {
        statusMessages.put(OrderStatus.PENDING, "订单正在处理中");
        statusMessages.put(OrderStatus.SHIPPED, "订单已发货");
        statusMessages.put(OrderStatus.DELIVERED, "订单已送达");
        statusMessages.put(OrderStatus.CANCELLED, "订单已取消");
    }

    public static String getMessage(OrderStatus status) {
        return statusMessages.get(status);
    }
}