import java.util.Scanner;
class PlayableMonster extends Monster {
  ... //Previous code 
  public void nextAction(){
    System.out.println("north or south?");
    Scanner sc = new Scanner(System.in);
    String line = sc.nextLine();
    if(line.startsWith("north"))
      this.move(0,-1);
    else if(line.startsWith("south"))
      this.move(0,1);
  }
}