Scala编程中常见错误：Error:(24, 29) value foreach is not a member of java.util.Set[String]

问题: 在Scala编程开发中, 常常会出现相似以下的错误, Error:(24, 29) value foreach is not a member of java.util.Set[String]     for (key <- reducedList.keySet) {                             ^ 或 Error:(21, 22) value filter i

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