Store Value By reference in collection (Java)

In java value are store in collection are by refernece . If two map are refer to same object . and if one object is become null it does not effect value of other one where updation in any value effect each other.

for Example
Hashmap<String,String> map = new Hashmap<String,String>();
Hashmap<String,String> map1= map;

if we add a value in map1 i.e
map1.add("name","amitrai");
Then value of map variable is aslo change but

if we make map1 null i.e
map1 = null;
it does not affect value of map because it store value by refrence

so if we print map.get("name");
we do not get anay exeception , it will simply print amit ........