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// A superclass reference can refer to a subclass object.

class X2 {

int a;

public X2(int i) {

// TODO Auto-generated constructor stub

a = i;

}

}

class Y2 extends X2 {

int b;

public Y2(int i, int j) {

// TODO Auto-generated constructor stub

super(j);

b = i;

}

}

public class SupSubRef {

public static void main(String[] args) {

// TODO Auto-generated method stub

X2 x = new X2(10);

X2 x2;

Y2 y = new Y2(5, 6);

x2 = x; // OK, both of same type.

System.out.println("X2.a: " + x2.a);

x2 = y; // still ok because Y2 is derived from X2. Both of somewhat same type.

System.out.println("X2.a: " + x2.a);

// X references know only about X members

x2.a = 19; // OK

// x2.b = 27; // Error, X does not have a b member.

}

}