Java ArrayList copy constructor

Question

I have an object anObject with two private member variables:

public class anObject {
    private String name;
    private ArrayList<String> myList = new ArrayList<String>();
}

I have a constructor:

public anObject() {
    name = "";
}

I have my copy constructors:

public anObject(anObject copy) {
this();
newObject(copy);
}

public void newObject(anObject copyTwo) {
    name = copyTwo.name;
    // How to deep copy an ArrayList?
}

But how can I "deep copy" all the elements of my ArrayList in copyTwo, to my this.myList?

I have looked at the other questions on SO but their ArrayLists all contain objects whereas mine just contains Strings. Thanks for any help!

If you want a deep copy for your list, you just need a foreach in your list — Vahid Vakily
– Vahid Vakily, Commented May 5, 2017 at 18:50

ΦXocę 웃 Пepeúpa ツ · Accepted Answer · 2017-05-05 19:03:37Z

4

create a new reference to list, since your list is holding strings and strings are immutable you can do:

List<String> copyString = new ArrayList<>(original);

edited May 5, 2017 at 19:03

answered May 5, 2017 at 18:52

ΦXocę 웃 Пepeúpa ツ

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6 Comments

Coder117 Over a year ago

So this won't be a problem with what I have been seeing as a "Shallow Copy"? I don't want changes to one object to affect the other.

davidxxx Over a year ago

You are using a List of String. It cannot .

Coder117 Over a year ago

@davidxxx great Thanks!

Mick Mnemonic Over a year ago

Java strings are immutable, so that won't be a problem. If the list would contain mutable reference types, you would need to deep copy the elements as well.

Coder117 Over a year ago

@MickMnemonic Gotcha. And do I have to create a List or can I still use an ArrayList?

|

Prateek Mishra · Accepted Answer · 2017-05-05 18:54:39Z

1

You can deep copy using a new collection. Changes in new collection won't affect the previous list

List<String> copyTwo= new ARrayList<String>();
copyTwo.addAll(myList );

edited May 5, 2017 at 18:54

answered May 5, 2017 at 18:51

Prateek Mishra

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4 Comments

assylias Over a year ago

Why not: List<String> copyTwo= new ArrayList<String>(myList);?

CraigR8806 Over a year ago

Hi, here on stackoverflow, we don't just provide the questioneer with code. We provide them with an explanation of why this will solve their problem, or how it works. Please edit your answer to reflect this mentality :)

Prateek Mishra Over a year ago

another option to do that

Coder117 Over a year ago

@assylias Do I have to use List or can I still use ArrayList?

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