class Node(vName: String, vAge: Int) {

  // Entity class

  var name: String = vName

  var age: Int = vAge

}

object TestGenerator {

  def main(args: Array[String]): Unit = {

    test()

  }

  def test(): Unit = {

    // This test case is to find out the max age node from each node's list

    // First, define the node 1,2,3

    val node1 = new Node("name-1", 1)

    val node2 = new Node("name-2", 2)

    val node3 = new Node("name-3", 3)

    // Second, def some List containing nodes

    val list1: List[Node] = List(node1, node2, node3)

    val list2: List[Node] = List(node1)

    val list3: List[Node] = List(node1, node2)

    val list4: List[Node] = List()

    val list5: List[Node] = Nil

    val list6: List[Node] = null

    // ==== Test Case 1 ====

    // In this test, the generator excluded the Nil and List() and null, and take the "node" out of headOption" which is Option[Node]

    // The returns are collected into node as Node

    val allList: Seq[List[Node]] = Seq(list1, list2, list3, list4, list5, list6)

    val result1 = for {

      list: List[Node] <- allList // The type List[Node] is necessary for this situation, it can help to filter out list6 (null)

      node <- list.sortWith(_.age > _.age).headOption

    } yield node

    for (r <- result1) {

      println(r.name)

    }

    println("======================================================")

    // *****************************************************************************

    // ==== Test Case 2 ====

    // In this test, use get() function to get back the list instead of Seq[List[Node]]

    def get(i: Int): List[Node] = {

      i match {

        case 1 => list1;

        case 2 => list2;

        case 3 => list3;

        case 4 => list4;

        case 5 => list5;

        case 6 => list6;

      }

    }

    // Define the array to contain the test lists

    // List 1-5 will be used for this test, but list6 (null) cannot be handled in this approach

    val arr = List(1, 2, 3, 4, 5) // list6 (null) cannot be handled thus only 1-5 here

    val result2 = for {

      i <- arr

      node <- get(i).sortWith(_.age > _.age).headOption

    } yield node

    for (r <- result2) {

      println(r.name)

    }

  }

}