I have a list of sets of pairs. If I use equal does it copy every set over?
List<HashSet<Pair>> list1 = new ArrayList<HashSet<Pair>>();
List<HashSet<Pair>> list2 = new ArrayList<HashSet<Pair>>();
list1.add(0, new HashSet<Pair>());
list1.add(1, new HashSet<Pair>());
list1.add(2, new HashSet<Pair>());
list1.add(3, new HashSet<Pair>());
If I do list2 = list1
, does it copy over perfectly? Because when I use it, it crashes.
Iterator<Pair> it1 = list2.get(0).iterator();
Iterator<Pair> it2 = list2.get(1).iterator();
Iterator<Pair> it3 = list2.get(2).iterator();
Iterator<Pair> it4 = list2.get(3).iterator();
No. The assignment doesn't copy anything, and instead updates the list2 reference to point to list1. So you are able to use list2 as if it were list1; however changes you make to 2 will be reflected in 1.
list2 = list1
This assignment simply assigns the reference list2
to point at the same List as list1
. (Note that there is only one list with two references to it.) If you want to copy the list, you need to use a copy constructor:
list2 = new ArrayList<HashSet<Pair>>(list1);
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