I'm very curious about how this thing works inside Android. I have a class with two List<> inside, instantiated at runtime and loaded with objects created while reading some data, I want to know what happens with those Lists in this situation:
Class A has List B and List C with many other initialized objects
inside.
Another different class get a reference of List C from a
method of Class A, like public List<myObject> GetList().
Somewhere in code, Class A is no longer used and application
signals that to garbage collector, setting object to null.
What happens with my List C that is referenced by other object? What happens with Object class A?
I've tried to track garbage collector with Logcat running apk in debugger step-by-step but no luck at all. Sometimes it frees memory, sometimes not, I couldn't pinpoint any specific behaviour.
If there is any object, that still has a path to root, containing a reference to another object, the referenced object will not be garbage collected. So if you create object A, that has a sub object A1. Then create object B and through what ever means pass a reference to A1 to object B. Even when object A is GC'd A1 will not be because object B still holds a reference. (In your example, A & B will be gc'd... C will not)
You can experiment with the mechanics behind garbage collection by telling the system explicitly to perform a collection at certain times with a System.gc(); call. Also you can override the finalize in object to see exactly when the given object is collected.:
@Override
protected void finalize() throws Throwable {
try {
Log.d("Learning about GC", "My Object has been GC'd." + this);
} finally {
super.finalize();
}
}
You can learn a lot through experimenting with objects, references, finalize and explicit calls for gc(). I would remove the overridden finalize call when you done testing.
The object of class A will be garbage collected during the next GC-cycle. List B will be GC'ed too. And List C will not be GC'ed because it can be reached from GC roots.
By default java creates an object by reference instead of by value. So, in this case if the garbage collector would pick up and empty all A B C and the then the other class that referenced C would be empty, since it didnt create a duplication of the class, it just referenced it.
