如何在基于枚举的交换机中处理默认情况？

Question

我有一个枚举,根据枚举类型评估字符串是否有效.使用开关执行验证.默认操作是这样的: default: return false;.

程序员添加了一个新类型并忘记更新isValid(..),导致isValid(..)每次评估答案时调用都返回false.

您认为处理它的正确方法是什么？

public enum AnswerType {
  TEXT("string"),
  INT("integer"),
  FLOAT("float");

  final String type;

  AnswerType(final String type) {
    this.type = type;
  }

  /**
   * Checks whether the given answer is valid for this answer type.
   * @param answer The provided answer.
   * @return true if the answer is valid; false otherwise.
   */
  public boolean isValid(final String answer) {

    switch (this) {
      case TEXT:
        return !StringUtils.isEmpty(answer);

      case INT:
        return NumberUtils.isDigits(answer);

      case FLOAT:
        return NumberUtils.isNumber(answer);

      default:
        return false; // Not sure this is best practise.
    }
  }
}

Answer 1

这是一个奇怪的设计(并且你的代码不能达到默认情况)...为什么不把方法放在每个枚举常量中呢？

public static enum AnswerType {
  TEXT("string") {
    public boolean isValid(String answer) { return !StringUtils.isEmpty(answer); }
  },
  INT("integer") {
    public boolean isValid(String answer) { return NumberUtils.isDigits(answer); }
  },
  FLOAT("float") {
    public boolean isValid(String answer) { return NumberUtils.isNumber(answer); }
  };

  private final String type;

  AnswerType(final String type) {
    this.type = type;
  }

  /**
   * Checks whether the given answer is valid for this answer type.
   *
   * @param answer The provided answer.
   *
   * @return true if the answer is valid; false otherwise.
   */
  public abstract boolean isValid(final String answer);
}

或者,如果您使用Java 8,则可以进一步简化代码:

public static enum AnswerType {
  TEXT("string", s -> !StringUtils.isEmpty(s)),
  INT("integer", NumberUtils::isDigits),
  FLOAT("float", NumberUtils::isNumber);

  private final String type;
  private final Predicate<String> isValid;

  AnswerType(final String type, Predicate<String> isValid) {
    this.type = type;
    this.isValid = isValid;
  }

  /**
   * Checks whether the given answer is valid for this answer type.
   *
   * @param answer The provided answer.
   *
   * @return true if the answer is valid; false otherwise.
   */
  public boolean isValid(final String answer) {
    return isValid.test(answer);
  }
}