Scala function - Type mismatch. Required: Null. Found: String-CodePudding

I have a problem with type mismatch in Scala Function. Compiler returns an error:

  def isLarger(inputNum: Int) = {
      var res = null
      if (inputNum.>(10)) {
          res = "aaa"
        }
      res
      }

If inputNum larger than 10, return String "aaa" if not, return null. But Type match. Why? Any idea what could be the problem?

CodePudding user response：

Try to add type declaration

var res: String = null

By the way, you don't need a var. If-else is an expression

def isLarger(inputNum: Int) = {
  val res: String = 
    if (inputNum > 10)
      "aaa"
    else null
  res
}

The concept of absent value is better expressed with Option rather than null

def isLarger(inputNum: Int) =
  if (inputNum > 10)
    Some("aaa")
  else None