Add elements of one ArrayList to another ArrayList

Question

Is it possible to add the elements of one Arraylist to another Arraylist? For example if an Arraylist has elements 3,6,3,8,5 in index 0,1,2,3,4, now I want to add 3,6,3,8,5 to another ArrayList in index 0, is it possible?

ArrayList<String> num = new ArrayList<String>();
 num.add("3");
 num.add("6");
 num.add("3");
 num.add("8");
 num.add("5");
ArrayList<String> result = new ArrayList<String>();
 for (int i = 0; i < num.size(); i++)
 {
        result.addAll(i,num);   
 }

I have tried this but it is not working. what i want is when i try System.out.println(result.get(0)); result must be [3 6 3 8 5].

Please explain what you want. I suspect people are confused. What do you want result to be after you're done? — ajb
– ajb, Commented Apr 4, 2015 at 5:43
Check this link for ArrayList of ArrayList stackoverflow.com/questions/25147799/… — N Kaushik
– N Kaushik, Commented Apr 4, 2015 at 6:37

Stephen C · Accepted Answer · 2015-04-04 06:37:33Z

35

I think what you are trying to do is this:

for (int i = 0; i < num.size(); i++) {
    result.add(i, num.get(i)); 
}

Or maybe just this:

result.addAll(num);

What your current code does is you add all of num to result many times ... at successive starting positions. That is ... strange.

UPDATE

What i want is when i try System.out.println(result.get(0)); result must be [3 6 3 8 5].

Ah ... I get it ... you are trying to create a list of strings where the strings are representations of the input lists:

Do this:

for (int i = 0; i < num.size(); i++) {
    result.add(i, num.toString()); 
}

This will give you the output you are asking for.

Another possibility is that you want a list of lists of strings:

ArrayList<ArrayList<String>> result = new ArrayList<>();
for (int i = 0; i < num.size(); i++) {
    result.add(i, num); 
}

That will also give you the output you are asking for ... though for a different reason.

edited Apr 4, 2015 at 6:37

answered Apr 4, 2015 at 5:43

Stephen C

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5 Comments

koshish kharel Over a year ago

this simply copy element from one Arraylist to another. what i want is to copy element of num to result in index 0.

glglgl Over a year ago

@koshishkharel Did the next intitively logig step to try work? That would be result.addAll(0, num).

koshish kharel Over a year ago

@glglgl what if num takes input from file and file contains multiple line. here first line of file is 3,6,3,8,5. each line should be added in different index of result.

koshish kharel Over a year ago

@stephen C what i trying to do is read the file containing multiple line like 3,6,3,8,5 and add it to Arraylist, my code is adding 3,6,3,8,5 in index 0,1,2,3,4 but i want to add first line in index 0 and second line in index 1 and so on. your suggestion is adding every line to index 0. what can i do?

Stephen C Over a year ago

@koshishkharel - What I suggest you do is ... >>think about it<< ... and work it out for yourself. You are a Java programmer, aren't yoo?

singhakash · Accepted Answer · 2015-04-04 06:09:29Z

4

To simply copy all elements you can do

ArrayList<String> result = new ArrayList<String>(num);

Demo

and if you want to copy all the elements at a particular index you have to change the result ArrayList

ArrayList<List<String>> result = new ArrayList<List<String>>();
result.add(0, num);   // 0 is the index

Demo

edited Apr 4, 2015 at 6:09

answered Apr 4, 2015 at 5:40

singhakash

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Comments

user9562951 · Accepted Answer · 2018-03-28 09:00:21Z

4

ArrayList<String> num = new ArrayList<String>();
 num.add("3");
 num.add("6");
 num.add("3");
 num.add("8");
 num.add("5");
ArrayList<String> result = new ArrayList<String>();
result.addAll(num);

answered Mar 28, 2018 at 9:00

user9562951

411 bronze badge

Comments

jeremie · Accepted Answer · 2015-04-04 05:39:05Z

1

Your result list needs to be nested. It should have this kind of form:

List<List<Integer>> result = new ArrayList<>();

You can then just do that

result.add(0, num);

answered Apr 4, 2015 at 5:39

jeremie

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1 Comment

jeremie Over a year ago

note that if you're using a version below java 7, you'll have to declare result like this: List<List<Integer>> result = new ArrayList<List<Integer>>();

Saurabh Jhunjhunwala · Accepted Answer · 2015-04-04 06:09:18Z

1

do not use all method if you are putting it inside a loop, you should use add

if at all you want to use addAll put it outside the loop.

answered Apr 4, 2015 at 6:09

Saurabh Jhunjhunwala

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Comments

Anusha B · Accepted Answer · 2016-12-14 17:51:47Z

1

ArrayList<String> obj1 = new ArrayList<String>();

obj1.add("3");
obj1.add("6");
obj1.add("3");
obj1.add("8");
obj1.add("5");

ArrayList obj2 = new ArrayList();

obj2.add(0, obj1);;

System.out.println("Size of the arraylist is --> "+obj2.size());

System.out.println("Value at index 0 --> "+obj2);

answered Dec 14, 2016 at 17:51

Anusha B

111 bronze badge

Comments

malli · Accepted Answer · 2015-04-04 05:32:17Z

-1

Try this sample code

ArrayList<ArrayList<String>> nodes = new ArrayList<ArrayList<String>>();
  ArrayList<String> nodeList = new ArrayList<String>();
   nodes.add(nodeList);

answered Apr 4, 2015 at 5:32

malli

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1 Comment

malli Over a year ago

tutorialhall.com/2015/03/…

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