从Java堆收集旧对象

Question

I have Order_Item class instance, and these are paths to GC Roots (excluding phantom/weak/soft references):

I have few questions:
1) I'm not sure if the Order_Item will be garbage collected.
I tried to run System.gc(), and the object remained in heap.
Is it allowed to be collected, according to provided image?

2) What "Native Stack" mean? As far as I understood, it's accounted as GC root. http://help.eclipse.org/mars/index.jsp?topic=%2Forg.eclipse.mat.ui.help%2Fconcepts%2Fgcroots.html Why some object (ie Order 0x782032cf8) is kept in "Native Stack"?

3) If I have reference from GC Root to object A, that object will not be garbage collected? Right?
And if so, my Order_Item object can't be garbage collected?

4) If 3 is right, how may I find what keeps objects 0x7821da5e0 and 0x782032cf8, and how to dereference/remove them?

Answer 1

You cannot really force the garbage collector to delete a given object. You know that the object is kept alive as long as it is reachable by references from the given point in the program. But if the object gets "collectable", it might be collected soon, but if there is no pressure on memory, it may fool around for a long time.

Usually, there is not reason to really delete objects if there is enough memory. The only exception I know are passwords. Here, you use a char array and overwrite it with nonsense once you used it.

For the native stack: Your link indicates that the native stack keeps external resources, eg files.