tsk5.java

package some;

public class tsk5 {

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

 public static void main(String[] args) {
 //noinspection ConstantConditions
 prt(A.a == null);
 prt(B.gb() == null);
 prt(C.gc() == null);
 }

 @SuppressWarnings("InstantiationOfUtilityClass")
 static class A {
 static final A a = new A();
 private A() {}
 }

 static class B {
 private static B b = null;
 private B() { b = this; }
 static B gb() { return b; }
 }

 static {
 try {
 final var b = B.class.getDeclaredFields()[0];
 b.setAccessible(true);
 b.set(null, B.class.getDeclaredConstructors()[0].newInstance());
 } catch (Exception a) { a.printStackTrace(); }
 }

 static class C {
 private static C c = null;
 private C() {}
 static C gc() { return c == null ? c = new C() : c; }
 }
}