有没有办法清除 arraylist 但不尊重内存引用？

Question

This is the relevant part of my code:

    List<List<String>> list2 = new ArrayList<>();
    public void process(List<String> z) {
        if (z.size() > 0) {
            String x = z.get(0);

            List<String> temp = new ArrayList<>();

            z.stream().filter(e -> !e.equals(x)).forEach(e -> {
                // some operations on temp
            });

            list2.add(temp);                   // adding temp to list2

            z.removeIf(e -> temp.contains(e));
            temp.clear();                      // clearing temp

            z.forEach(System.out::println);
            list2.forEach((System.out::println));   // empty list2

            process(z);
            list2.forEach(e -> process(e));
    }

I have to clear temp before recursively calling process .
Issue here is, my list2 gets empty, upon clearing temp .
As i am using temp inside the lambda expression, i cannot re-assign it as null or new ArrayList<>() (otherwise it would have worked).

I thought of creating a new List and copying between temp and new List, but it doesn't feel like a proper approach.
Is there any other way to do this?

Answer 1

While this answer addresses the issue of clearing the list when it's in another list, the real answer is in Turing85's comment that there's no need to clear temp , since temp is a local.

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If you want to clear temp without clearing the entries on that list that you've inserted in list2 , you can't insert temp into list2 and then clear temp , because temp and the entry in list2 both point to the same list.

Instead, insert a copy:

list2.add(new ArrayList<>(temp));

Then when you clear temp , the new list you've put in list2 will be unaffected.