adding elements to the ArrayList nested inside another Arraylist

Question

I have nested ArrayList that looks like that in Java:

myArrayList = [element1, element2, [element3]]

I would like to add elements so the ArrayList will look like that:

myArraylist = [element1, element2, [element3, element4, element5]]

I tried to use;

myArrayList.get(2).add(elemet4);
myArrayList.get(2).add(elemet5);

but as a result I got:

myArraylist = [element1, element2, [element3], element4, element5]

Any hints how to resolve that will be much appreciated.

edit: My bad, I should have attached Java code and avoid misleading you guys. Anyway here it is:

ArrayList<ArrayList<String>> finalArray = new ArrayList<ArrayList<String>>();
ArrayList<String> finalArrayTempCopy = new ArrayList<String>();
ArrayList<Integer> transactionTemp = new ArrayList<Integer>();

private ArrayList<Integer> addTransaction(){

        System.out.println("Enter transaction amount:");
        int amount = scanner.nextInt();
        scanner.nextLine();
        transactionTemp.add(Integer.valueOf(amount)); 
        return transactionTemp;
}
private int searchName(String name){
        int indexImienia = customerName.indexOf(name);
        return indexImienia;
    }

public void sumUp(){
        String name = "Tom";
        String branch = "First";
        int indexImienia = searchName(name);
        String transactionsAsString = transactionTemp.toString();   
        finalArrayTemp.add(name);
        finalArrayTemp.add(branch);
        finalArrayTemp.add(transactionsAsString);
        finalArrayTempCopy = new ArrayList<String>(finalArrayTemp);

        finalArray.add(indexImienia, finalArrayTempCopy);
}

Later in the code if I want to add single transaction I use the following method

public void addSingleTransaction(){
int indexImienia = 0;
int amount =20;
finalArray.get(indexImienia).add(2, String.valueOf(amount));
}

Editing my post I realised that the problem might lie with converting ArrayList into string and adding it to finalArray as string. Anyway, I will be grateful for your insight.

Could you please show the exact declaration of you ArrayList? I got a suspicion that you either use ArrayList<Object> or a raw type... — Turing85
– Turing85, Commented May 23, 2017 at 17:41
The pseudocode you give should work, so there's probably a bug in your actual code. Can you make an MCVE (Minimal, Complete, Verifiable Example)? — Sean Van Gorder
– Sean Van Gorder, Commented May 23, 2017 at 17:48

gajju_15 · Accepted Answer · 2017-05-24 06:40:56Z

2

i think you looking for

    List<Object> list1=new ArrayList<Object>();
    List<Object> list=new ArrayList<Object>();
    list.add("element1");
    list.add("element2");

    list1.add("element3");
    list.add(list1);

    List<Object> listobj=(List<Object>) list.get(2);

    listobj.add("element4");
    listobj.add("element5");
    System.out.println(list);

you are adding element to your parent list not your nested list, for which you have to store the reference of your nested list, then you can add other elements.

edited May 24, 2017 at 6:40

answered May 23, 2017 at 18:26

gajju_15

5274 silver badges17 bronze badges

Sign up to request clarification or add additional context in comments.

3 Comments

Vinod Over a year ago

For list variable, you can clone of list1.

gajju_15 Over a year ago

I think cloning is not required.

Vinod Over a year ago

I got requirement.

slal · Accepted Answer · 2017-05-23 17:56:01Z

1

Seems like you are looking for:

 ArrayList<Object> myArrayList = new ArrayList<Object>();
 ArrayList<Integer> list1 = new ArrayList<Integer>;

 myArrayList.add(element1);
 myArrayList.add(list1);

Or

ArrayList<ArrayList<Integer>> myArrayList = new ArrayList<ArrayList<Integer>>();
ArrayList<Integer> list1 = new ArrayList<Integer>;
ArrayList<Integer> list2 = new ArrayList<Integer>;

list1.add(element1);
list2.add(element2);
list2.add(element3);

myArrayList.add(list1);
myArrayList.add(list2);

Assuming, element is an Integer

edited May 23, 2017 at 17:56

answered May 23, 2017 at 17:42

slal

2,8672 gold badges20 silver badges30 bronze badges

Comments

GP007 · Accepted Answer · 2017-05-23 18:16:38Z

As per the psuedo code shared, There is some issue with your main array declaration.

ArrayList can only have one type of data in it. Therefore, your declaration of array can be like :

ArrayList<Element> arr = new ArrayList<Element>();

or to store List in it:

ArrayList<ArrayList<Element>> ar2 = new ArrayList<ArrayList<Element>>();

If you wish to store both type of values in same structure you can use Object for storing any type of value, since it is the root of all classes. In this case your declaration will be something like:

     ArrayList<Object> arrOuter = new ArrayList<Object>();

     Element e1 = new Element();
     Element e2 = new Element();
     arrOuter.add(e1);
     arrOuter.add(e2);

     ArrayList<Element> arrNested  = new ArrayList<Element>();
     Element e3 = new Element();
     arrNested.add(e3);

     arrOuter.add(arrNested);

But in this case you can not directly call add method on data returned by arrOuter, since the data returned is of Object class. You have to explicitly cast it to list and then add another data.

 Element e4 = new Element(); 
 Element e5 = new Element();
 ((ArrayList) arrOuter.get(2)).add(e4);
 ((ArrayList) arrOuter.get(2)).add(e5);

Ganesh · Accepted Answer · 2023-03-09 16:43:11Z

0

List<List<Integer>> list=null;
public FirstGraph(int vertex) {
   list=new ArrayList<List<Integer>>(5);
    int i=0;
    while(i<vertex) {
        List<Integer> a = new ArrayList<Integer>();
        list.add(a);
        i++;
    }

}

answered Mar 9, 2023 at 16:43

Ganesh

11 bronze badge

1 Comment

Community Over a year ago

As it’s currently written, your answer is unclear. Please edit to add additional details that will help others understand how this addresses the question asked. You can find more information on how to write good answers in the help center.

Collectives™ on Stack Overflow

adding elements to the ArrayList nested inside another Arraylist

4 Answers 4

3 Comments

Comments

Comments

1 Comment

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

4 Answers 4

3 Comments

Comments

Comments

1 Comment

Your Answer

Sign up or log in

Post as a guest

Linked

Related