没有引用对象时的Java垃圾回收

Question

For example with the following code,

class Dog {
    Dog parent;
    Dog (Dog parent) {
        this.parent = parent;
    }

    Dog makeDog (Dog dog) {
        return new Dog(new Dog(new Dog(dog)));
    }
}

public class test {
    public static void main(String[] args) {
        Dog dog = new Dog(null);
        dog = dog.makeDog(dog);
        Dog anotherDog = new Dog(dog);
        /*
         * many lines of code
         */
        if (anotherDog.parent.parent.parent.parent.parent == null) {
            System.out.println("null");
        }
    }
}

Is this program guaranteed to print null?

Most of my programs are in C, and this is the way I build linked lists, trees, graphs et cetera. But I am really not sure how the Java garbage collector will deal with such code, so in the real program, I chose to store the references elsewhere so the GC can know that the objects are indeed not garbage.

Any helps are welcome.

Answer 1

As long as an object is reachable through a chain of strong references from a GC root (a thread stack, or a static variable), it will not be garbage collected. It doesn't matter how convoluted the path to the object is.