static object 经历的所有值是否在 memory 中占用空间，而 ZA2F2ED4F8EBC0661C21A291Z 已加载？

Question

I know that static variables are stored in a specific place in memory. Whenever you declare an object as static, that object will never be recycled by gc as long as that class is loaded by the classloader.. so far so good.

But imagine that the variable that I defined as static has an internally non-static list, so even though the object itself will never be recycled, will that list be recycled normally? And even if I assign a new instance to a static object, will the old value not be recycled? Would all the values that this object went through take up space in memory?

Answer 1

The garbage collector starts its scanning from gc roots , one such root is a static field.

So a GC will traverse all entries that "start" from this root, for example:

   SomeStaticInstance
          |
         \ /
     NonStaticList

If NonStaticList is reachable ( marking phase of the gc phases takes care of this), it is considered alive and thus not eligible for GC . If it is not reachable, it is eligible for collection. Notice that if it is not reachable, mark phase will not even traverse anything that might have references from NonStaticList :

 NonStaticList
       |
      \ /
    RefHere

So RefHere is not going to be scanned. It might get scanned if it has references from somewhere else to it, but not from NonStaticList .