Gson().toJson() output

data class Student(  
   @SerializedName("key_name") 
   var name: String? = null, 
   @SerializedName("key_address") 
   var address: String? = null) {
}

val student = Student("Mark", "London, 12000") // object
val json = Gson().toJson(student)  // json string

/** Output json will be like below **/
{
  "key_name": "Mark",
  "key_address": "London, 12000"
}