Certificacao - GC

[maxguzenski]

ola pessoal,
estava estudando o livro da Kathy Sierra, capítulo 7 (Collections e GC)
e quando fui fazer os testes (15 perguntas no final do capitulo) me deparei com a seguinte questão

Which statement is true?
A. All objects that are eligible for garbage collection will be garbage collected by the garbage
collector.
B. Objects with at least one reference will never be garbage collected.
C. Objects from a class with the finalize() method overridden will never be garbage
collected.
D. Objects instantiated within anonymous inner classes are placed in the garbage collectible heap.
E. Once an overridden finalize() method is invoked, there is no way to make that object
ineligible for garbage collection.

Eu responti que a resposta certa era “B”, mas errei… segue a explicação do livro:
Correto: “D” All objects are placed in the garbage collectible heap.
Incorreto: “A” is incorrect because the garbage collector makes no guarantees. “B” is incorrect because islands of isolated objects can exist. “C” is incorrect because finalize() has no such mystical powers. “E” is incorrect because within a finalize() method, an object’s reference can be passed back to a live thread.

alguem entendeu porque?

[maxguzenski]

ah, a explição so sobre “islands of isolation” segue a baixo:

Isolating a Reference There is another way in which objects can become eligible for garbage collection, even if they still have valid references! We think of this scenario as islands of isolation. A simple example is a class that has an instance variable that is a reference variable to another instance of the same class. Now imagine that two such instances exist and
that they refer to each other. If all other references to these two objects are removed, then even though each object still has a valid reference, there will be no way for any live thread to access either object. When the garbage collector runs, it will discover any such islands of objects and will remove them. As you can imagine, such islands can become quite large, theoretically containing hundreds of objects. Examine the following code:

public class Island {
  Island i;
  public static void main(String [] args) {
      Island i2 = new Island();
      Island i3 = new Island();
      Island i4 = new Island();
      i2.i = i3; // i2 refers to i3
      i3.i = i4; // i3 refers to i4
      i4.i = i2; // i4 refers to i2
      i2 = null;
      i3 = null;
      i4 = null;
     // do complicated, memory intensive stuff
  }
}

When the code reaches // do complicated, the three Island objects
(previously known as i2, i3, and i4) have instance variables so that they refer to each other, but their links to the outside world (i2, i3, and i4) have been nulled. These three objects are eligible for garbage collection.

[ricardolecheta]

interessante!!! “islands of isolation”

eu fiquei na duvida entre a B e D, mas marquei a B tb