OnJava8-Examples/generics/CovariantArrays.java

// generics/CovariantArrays.java
// <20>2016 MindView LLC: see Copyright.txt
// We make no guarantees that this code is fit for any purpose.
// Visit http://mindviewinc.com/Books/OnJava/ for more book information.

class Fruit {}
class Apple extends Fruit {}
class Jonathan extends Apple {}
class Orange extends Fruit {}

public class CovariantArrays {
  public static void main(String[] args) {
    Fruit[] fruit = new Apple[10];
    fruit[0] = new Apple(); // OK
    fruit[1] = new Jonathan(); // OK
    // Runtime type is Apple[], not Fruit[] or Orange[]:
    try {
      // Compiler allows you to add Fruit:
      fruit[0] = new Fruit(); // ArrayStoreException
    } catch(Exception e) { System.out.println(e); }
    try {
      // Compiler allows you to add Oranges:
      fruit[0] = new Orange(); // ArrayStoreException
    } catch(Exception e) { System.out.println(e); }
  }
}
/* Output:
java.lang.ArrayStoreException: Fruit
java.lang.ArrayStoreException: Orange
*/