cannot apply java lang integer android code example

Example: cannot apply java lang integer android

val a = result.text.toString()
 val b = resultHist1.text.toString()

 if(!a.isNullOrEmpty() &&  !b.isNullOrEmpty() ){
    val a = a.toInt()
    val b = b.toInt()
    calcHist1.text = (a+b).toString()
   }
   else
   {
   calcHist1.text = ""
   }