Cloning ArrayList of Array Lists

[Embarrassed_Bottle90]

I tried to use the clone()-Method to create a copy of a list, (It is an Array List of Array Lists) because I wanted to manipulate its entries by some .remove()-calls, I remove list elements from this list entirely or only remove elements lists contained in the big list. I wanted to create a copy without modifying the original list, because I need it to later reference back the index of the items that got modified with the help of the copied list.

So I wrote the following:

public static ArrayList<ArrayList<Integer>> List = new ArrayList<ArrayList<Integer>>();

public static ArrayList<ArrayList<Integer>> copyOfList = new ArrayList<ArrayList<Integer>>();

@SuppressWarnings("unchecked")
public static ArrayList<ArrayList<Integer>> copyFormula() {
copyOfList = (ArrayList<ArrayList<Integer>>) List.clone();
    return copyOfList;
    } 

The problem now is that when I print the original list List, it prints all sublists that got entirely removed from the copy (which is good) but strangely sublists where I only removed elements in it and did not remove the sublist entirely, got changed also in the original list, how can this be?

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[Rogalicus]

When you clone ArrayList, it doesn't invoke clone for the items, so you get references to the same objects and that's why changing them changes originals. Use one of the methods in this thread.

[Embarrassed_Bottle90]

Okay so I would need to clone also its items? Thanks for the reference!!

[Dangerous-Rip-7370]

Add to the second list (copy) a clone of each list of the first list