OnJava8-Examples/polymorphism/CovariantReturn.java

// polymorphism/CovariantReturn.java
// (c)2021 MindView LLC: see Copyright.txt
// We make no guarantees that this code is fit for any purpose.
// Visit http://OnJava8.com for more book information.

class Grain {
  @Override public String toString() {
    return "Grain";
  }
}

class Wheat extends Grain {
  @Override public String toString() {
    return "Wheat";
  }
}

class Mill {
  Grain process() { return new Grain(); }
}

class WheatMill extends Mill {
  @Override Wheat process() {
    return new Wheat();
  }
}

public class CovariantReturn {
  public static void main(String[] args) {
    Mill m = new Mill();
    Grain g = m.process();
    System.out.println(g);
    m = new WheatMill();
    g = m.process();
    System.out.println(g);
  }
}
/* Output:
Grain
Wheat
*/