Deep copy of an ArrayList which collects ArrayLists

Question

i need a method that makes a deep copy..it takes as parameter ArrayList<Arraylist<Integer>>m and makes a deep copy to another ArrayList which collects also ArrayLists... Everything needs to be deep copied.But no loops only recursively...

Could someone help me how to do it ?

Did you take a look at stackoverflow.com/questions/3291830/… — hemanth
– hemanth, Commented Feb 2, 2014 at 23:35
well i can recursively make a deep copy of an arraylist..but , i dont know how to do since arraylist has arraylists inside..i cant use the arraylists copy constructor because it is a shallow copy.. — tlq
– tlq, Commented Feb 2, 2014 at 23:40

Gábor Bakos · Accepted Answer · 2014-02-03 09:09:33Z

1

I think the following code like below satisfies your constraints and similar to what you want to achieve:

public ArrayList<ArrayList<Integer>> deepCopy(ArrayList<ArrayList<Integer>> list) {
    ArrayList<ArrayList<Integer>> ret = new ArrayList<ArrayList<Integer>>();
    deepCopy(list.iterator, ret);
    return ret;
}

private void deepCopy(Iterator<ArrayList<Integer>> it, ArrayList<ArrayList<Integer>> ret) {
    if (it.hasNext()) {
        ret.add(new ArrayList(it.next()));
        deepCopy(it, ret);
    }
}

It just visits the list and creates new lists recursively.

With Integers there are no interesting uses cases though... Is this homework?

edited Feb 3, 2014 at 9:09

answered Feb 2, 2014 at 23:51

Gábor Bakos

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2 Comments

tlq Over a year ago

it does actually copy all integer values into one arraylist inside of arraylist.the other ones created but inside of them empty..Do i see something wrong here?

Gábor Bakos Over a year ago

"but inside of them empty", sorry, I do not understand this part of your statement. The copy constructor creates a new array with the values. It is true, that the Integer instances will remain the same. Although the idea I presented above would work there too. (Although I would use Integer.valueOf(...) instead of new Integer(...), so probably there would be not much difference.)

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