class X { 
  int a; 
 
  X(int i) { a = i; } 
} 
 
class Y extends X { 
  int b; 
 
  Y(int i, int j) { 
    super(j); 
    b = i; 
  } 
} 
 
class NadPodRef { 
  public static void main(String args[]) { 
    X x = new X(100); 
    X x2;  
    Y y = new Y(15, 25); 
 
    x2 = x; // spravne prirazeno 
    System.out.println("x2.a: " + x2.a); 
 
    x2 = y; // take mozno priradit
    System.out.println("x2.a: " + x2.a); 
 
    x2.a = 22; // OK 
//    x2.b = 21; // Chybne X nema prvek b 
  } 
}