Java协变返回类型

class Test{

   int data =100;

   Test demoMethod(){

      return this;

   }

}

public class Sample extends Test{

   int data =1000;

   Sample demoMethod(){

      return this;

   }

   public static void main(String args[]){

      Sample sam = new Sample();

      System.out.println(sam.demoMethod().data);

   }

}