class A {
  private B b = new B();
  @Override
  public String toString() {
      return "b "+b;
  }
}
 
class B {
  private A a = new A();
  @Override
  public String toString() {
      return "";
  }
}
 
class StackoverflowErrorTest {
  public static void main(String[] args) {
     A a = new A();
  }
}