类型不匹配错误声明类的列表 [英] type mismatch error declaring list of classes

问题描述

  def getValueAndItsType() : List[ (AnyRef, Class[_]) ] = {
    val dataSet1 = ("some string data", classOf[String])
    val dataSet2 = (new Thread(), classOf[Thread])
    val dataSet3 = (new NullPointerException(), classOf[NullPointerException])
    val dataSet4 = (5, classOf[Int])
    val list = List(dataSet1, dataSet2, dataSet3, dataSet4)
    list
  }

b $ b

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类型类型不匹配;发现：
List [（Any，Class [_>：Int with NullPointerException with Thread with
String]）]必需：List [（AnyRef，Class [_]）]

Type type mismatch; found : List[(Any, Class[_ >: Int with NullPointerException with Thread with String])] required: List[(AnyRef, Class[_])]

---

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If dataSet4 is removed from List, the compile time error disappears

请注意，Class [_]有什么问题。是不是
相当于Java中的Class [？]我很感激，如果你还建议
正确的声明这样做..

Please suggest, what is wrong with Class[_]. Isn't it equivalent to Class[?] in java ? I appreciate, if you also suggest correct declaration for doing this..

推荐答案

在 Scala 中：

• 任何 类类的根。
，它延伸自 Any 。

• AnyVal 所有值类型的类别。它延伸自任何


• Null 。
/ strong>包括 Null

• Any is the root of the Scala class.
• AnyRef is the root of the class of reference types, it extends from Any.
• AnyVal is the root class of all value types. it extends from Any
• Null is a subtype of all reference types.
• Nothingis a subtype of all other types including Null

扩展任何，包括 AnyRef：引用类型和 AnyVal：values类型。

def getValueAndItsType() : List[ (Any, _ <: Any) ] = {
    val dataSet1 = ("some string data", classOf[String])
    val dataSet2 = (new Thread(), classOf[Thread])
    val dataSet3 = (new NullPointerException(), classOf[NullPointerException])
    val list = List(dataSet1, dataSet2, dataSet3)
    list
}

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