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mister_svinia
Asked:2023-09-30 22:49:23 +0000 UTC2023-09-30 22:49:23 +0000 UTC

如何将 switch-case 与实际静态数据一起使用？

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有一个存储类是这样的：

public class CommandsIntentions {
    static Command ADMIN_CHANNELS_CREATE = new Command(new String[]{"ADMIN", "CHANNELS", "CREATE"}, DataCommands.ChannelCreate.class);
    static Command ADMIN_CHANNELS_USERS_JOIN = new Command(new String[]{"ADMIN", "CHANNELS", "USERS", "JOIN"}, DataCommands.ChannelUsersJoin.class);
    static Command ADMIN_CHANNELS_USERS_APPEND = null; // TODO
    static Command USER_CHANNELS_MESSAGES_POST_NEW = new Command(new String[]{"USER", "CHANNELS", "MESSAGES", "POST", "NEW"}, DataCommands.ChannelMessagesPostNew.class);
}

存储外壳是：

public class Command {
    String[] intents;
    Class pattern;

    public Command (String[] intents, Class pattern) {
        this.intents = intents;
        this.pattern = pattern;
    }
}

这是我的呼吁：

@Override
public void onMessage (WebSocket webSocket, String message) {
    Helper.MessagePacket packet = Helper.parsePacket(message);

    switch (packet.intention) {
        case CommandsIntentions.ADMIN_CHANNELS_CREATE.intents -> {
            break;
        }
        default -> {
            return;
        }
    }
}

但会抛出错误：

Constant expression required: 42

我还附上了包的解析：

public static class MessagePacket {
    final String hash;
    final String[] intention;
    final String preData;
    Object postData;

    public MessagePacket (String[] intention, String controlSum, String data) {
        this.intention = intention;
        this.hash = controlSum;
        this.preData = data;
    }

    public void parseData (Class pattern) {
        postData = JsonIterator.deserialize(preData, pattern);
    }
}

@Contract("_ -> new")
public static @NotNull MessagePacket parsePacket (@NotNull String packet) {
    String[] splitPacket = packet.split("%");

    return new MessagePacket(splitPacket[0].split("-"), splitPacket[1], splitPacket[2]);
}

主意

java

1 个回答

  1. Best Answer

    如果你真的想使用switch，那么你可以将类重写Command为枚举 ( enum) ，其中包含必要的字段和从意图数组中获取实例的方法，因为根据定义，枚举中的值是常量：

    public enum Command {
    ADMIN_CHANNELS_CREATE(new String[]{"ADMIN", "CHANNELS", "CREATE"}, DataCommands.ChannelCreate.class),
    ADMIN_CHANNELS_USERS_JOIN(new String[]{"ADMIN", "CHANNELS", "USERS", "JOIN"}, DataCommands.ChannelUsersJoin.class),
    ADMIN_CHANNELS_USERS_APPEND(new String[0], null), // TODO
    USER_CHANNELS_MESSAGES_POST_NEW(new String[]{"USER", "CHANNELS", "MESSAGES", "POST", "NEW"}, DataCommands.ChannelMessagesPostNew.class);

    private final String[] intents;
    private final Class pattern;

    private Command(String[] intents, Class pattern) {
        this.intents = intents;
        this.pattern = pattern;
    }

    // ... геттеры / toString ...

    // пример реализации -- сравниваются массивы целиком
    public static Command byIntents(String[] intents) {
        return Arrays.stream(Command.values())
            .filter(v -> Arrays.equals(v.intents, intents))
            .findFirst()
            .orElseThrow(NoSuchElementException::new);
    }
}

    因此，调用这样的命令可能如下所示：

    @Override
public void onMessage (WebSocket webSocket, String message) {
    Helper.MessagePacket packet = Helper.parsePacket(message);

    Command cmd = Command.byIntents(packet.intention); 
    switch (cmd) {
        case ADMIN_CHANNELS_CREATE, ADMIN_CHANNELS_USERS_JOIN -> {
            System.out.println("Команда админа: " + cmd);
        }
        default -> {
            System.out.println("Неизвестная команда, пока что не обрабатывается " + cmd);
        }
    }
}

    我想注意break经典运算符中使用的内容switch（case后面使用冒号），以便代码不会“穿过”“cases”中的不同标签。
    当使用“新”语法switch- 表达式（在 后面带有箭头case）时break ，在这种情况下不需要运算符（没有可以提前退出的循环）。

    • 1

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