arrays - Java vector resizing could be problematic like in C++? -

if have, example, hashmap of type:

hashmap<string,arraylist<integer> > tag_posizioni; tag_posizioni.put( "a",new arraylist<integer>() );  tag_posizioni.get("a").add(3); 

so, have resized arraylist associated a tag; so, have new vector in different memory zone; next

tag_posizioni.get("a") 

could throw memory error (because reference pointing not valid memory zone) or jvm manage automatically situation changing reference? more sure doing

arraylist<integer> pos=tag_posizioni.get("a"); pos.add(3); tag_posizioni.put("a", pos); 

or useless?

there nothing wrong code, when call:

tag_posizioni.get("a").add(3); 

then tag_posizioni.get("a") returns reference object on add(3) called. object (arraylist) changes internal data structures, internaly not known - encapsulated. statement true if able somehow take reference internal data structure (which private prevent doing this).

i think asking whether adding alement arraylist might cause tag_posizioni.get("a") return non valid memory. under java there no such thing dangling pointers in c++, may have null reference. instance of array list referenced in tag_posizioni.get("a") not modify own reference in tag_posizioni hashmap.

in c++ situation quite same, when use std::unordered_map<std::string, std::vector<int>>, adding element std::vector<int> might allocate more memory vector whole process of reallocating buffer encapsulated. in c++ allowd take pointer internal vector memory not wise - , might result in undefined behaviour.