列表时会发生什么 <Integer> A =清单 <Integer> B？

Question

What happens when I do this:

List<Integer> listA = new ArrayList<Integer>();
List<Integer> ListB = new ArrayList<Integer>();

listA = ...filled with some data...
listB = ...filled with some other data...

listA.clear();
listA = listB;

Does values copies or just re-reference? If I now (after this code) call listA.clear() again , will listB clear as well?

Answer 1

Well, after listA = listB the variable listA references the same list as listB . There is no copy-constructor in Java like you have it in C++ etc.

Answer 2

只是引用的值将被复制，因此它们两个都将引用同一对象

Answer 3

Only primitive types are copied by value, if you do the above you'll have listA and listB referencing the same list, so whatever you do with listA will have the same effect on listB and vice-verse. and if you want to lose the reference just set one of the variables to null.

Answer 4

No, listA and listB are two different list of integers, They are not related to each other. If you do a clear() on the ListA , ListB will not be affected at all. In your case at the end ListA reference is changed and the variable is now pointed to ListB . So, Both of these variables point to one List that is ListB . So, any action on any of these references will have the same effects. ListA object is already empty, it contains nothing. and there is not any way to refer that object.