tsk8.java

package some;

import java.util.ArrayList;

public class tsk8 {

 static void prt(Object a) { System.out.println(a); }

 @SuppressWarnings("StatementWithEmptyBody")
 public static void main(String[] args) throws Exception {
 var a = new Obvl() { @Override void nf() {
 prt("notifying...");
 super.nf();
 } };

 for (var i = 0; i < 5; i++,
 a.dd(() -> prt("update")) );
 a.nf();

 new Ctx(1);
 new Ctx(2);
 }

 ////////////////////////////////////////

 interface Obsr { void up(); }

 static abstract class Obvl {
 private final ArrayList<Obsr> _a = new ArrayList<>();
 void nf() { _a.forEach(Obsr::up); }
 final void dd(Obsr a) { _a.add(a); }
 }

 ////////////////////////////////////////

 static abstract class St {
 abstract int a();
 @Override public String toString() { return "" + a(); }
 }

 @SuppressWarnings("unused")
 static class St1 extends St { @Override public int a() { return 1; } }
 @SuppressWarnings("unused")
 static class St2 extends St { @Override public int a() { return 2; } }

 static class Ctx {
 Ctx(int a) throws Exception
 { prt(Class
 .forName(
 tsk8.class.getCanonicalName() +
 '$' +
 St.class.getSimpleName() + a)
 .getDeclaredConstructors()[0]
 .newInstance()); }
 }
}