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List Assignment vs. List.addAll()

Tom Henricksen
Ranch Hand

Joined: Mar 23, 2004
Posts: 136

What is the difference between these two methods of getting a list.


And this code.


Is there any difference in these. I ask as I tried the first approach with problems. When I tried the second it worked.

Thanks,
Tom
Ernest Friedman-Hill
author and iconoclast
Marshal

Joined: Jul 08, 2003
Posts: 24184
    
  34

The list you create with "new" in the first version is simply discarded when you make the assignment. Assigning to a Java variable in Java always completely discards any existing value without affecting it in any way. In this first version, you end up with localList pointing to the exact same List that object.getAList() returned -- meaning that if "object" still has a reference to that List, code in "object" could modify that list, and the changed would be visible via localList, and vice-versa, because they reference the same object.

In the second version, the elements of "object"'s list are put into a new list. Now either object can chnage their own list independently, without affecting the other one.


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Ilja Preuss
author
Sheriff

Joined: Jul 11, 2001
Posts: 14112
The difference in pictures:





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subject: List Assignment vs. List.addAll()