Add multiple items to an already initialized arraylist in Java

Question

My arraylist might be populated differently based on a user setting, so I've initialized it with

ArrayList<Integer> arList = new ArrayList<Integer>();

How can I add hundreds of integers without doing it one by one with arList.add(55);?

I already answer this question at stackoverflow.com/a/65368082/10304471 — Trishant Saxena
– Trishant Saxena, Commented Mar 7, 2021 at 6:05
@Trishant Saxena: No, not for the general case. More like rhino9's answer. Though the question is underspecified. — Peter Mortensen
– Peter Mortensen, Commented May 29, 2022 at 9:22
Do you want to add the same number hundreds of times? Or are they arbitrary numbers? — Peter Mortensen
– Peter Mortensen, Commented May 29, 2022 at 9:23
This must have been a duplicate in 2013, nearly 5 years after the launch of Stack Overflow. What is the canonical question? — Peter Mortensen
– Peter Mortensen, Commented May 29, 2022 at 9:39

Daniel Smith · Accepted Answer · 2016-02-10 01:15:23Z

124

If you have another list that contains all the items you would like to add you can do arList.addAll(otherList). Alternatively, if you will always add the same elements to the list you could create a new list that is initialized to contain all your values and use the addAll() method, with something like

Integer[] otherList = new Integer[] {1, 2, 3, 4, 5};
arList.addAll(Arrays.asList(otherList));

or, if you don't want to create that unnecessary array:

arList.addAll(Arrays.asList(1, 2, 3, 4, 5));

Otherwise you will have to have some sort of loop that adds the values to the list individually.

edited Feb 10, 2016 at 1:15

Daniel Smith

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answered Mar 5, 2013 at 1:00

scaevity

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4 Comments

batoutofhell Over a year ago

Really, I thought there was a better way? Oh well, looping works. Thx

scaevity Over a year ago

Yeah, unless you want to create a new list that is initialized with all your values (see my edit above), those are your options.

ucMax Over a year ago

The second one is definitely the most concise way of doing it

Cleaton Pais Over a year ago

Just what I was looking for

Peter Mortensen · Accepted Answer · 2022-05-29 08:54:10Z

33

What is the "source" of those integers? If it is something that you need to hard code in your source code, you may do

arList.addAll(Arrays.asList(1,1,2,3,5,8,13,21));

edited May 29, 2022 at 8:54

Peter Mortensen

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answered Mar 5, 2013 at 1:10

Adrian Shum

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1 Comment

krispy Over a year ago

This is definitely the most concise way of doing it.

Radiodef · Accepted Answer · 2018-06-28 02:25:42Z

15

Collections.addAll is a varargs method which allows us to add any number of items to a collection in a single statement:

List<Integer> list = new ArrayList<>();
Collections.addAll(list, 1, 2, 3, 4, 5);

It can also be used to add array elements to a collection:

Integer[] arr = ...;
Collections.addAll(list, arr);

edited Jun 28, 2018 at 2:25

answered Jun 10, 2018 at 20:06

Radiodef

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Comments

Fran G Aparicio · Accepted Answer · 2016-02-29 14:30:16Z

5

If you are looking to avoid multiple code lines to save space, maybe this syntax could be useful:

        java.util.ArrayList lisFieldNames = new ArrayList() {
            {
                add("value1"); 
                add("value2");
            }
        };

Removing new lines, you can show it compressed as:

        java.util.ArrayList lisFieldNames = new ArrayList() {
            {
                add("value1"); add("value2"); (...);
            }
        };

answered Feb 29, 2016 at 14:30

Fran G Aparicio

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3 Comments

user8063991 Over a year ago

Still requires multiple calls to add() and adds clutter even if it is compressed to one line

Fran G Aparicio Over a year ago

I would have the values in a String Ej. String theValues="1,20,2,1001"; (by hand or loaded from a File). Then pass it to Array: Integer[] theArray = theValues.split(",", -1); Once you have the array, it's easy to pass it to ArrayList: ArrayList<Integer> numbersList = new ArrayList<Integer>(java.util.Arrays.asList(theArray)); . (Not tested)

Alex Over a year ago

Here's a more detailed answer on why this works.

user197674 · Accepted Answer · 2021-06-15 00:58:27Z

2

Java 9+ now allows this:

List<Integer> arList = List.of(1,2,3,4,5);

The list will be immutable though.

answered Jun 15, 2021 at 0:58

user197674

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1 Comment

XyFreeman Over a year ago

Finally, this is the one line method to add multiple elements to one list. No loops, no additional lists, one simple line of code. Thank you.

Peter Mortensen · Accepted Answer · 2022-05-29 08:53:36Z

0

In a Kotlin way;

val arList = ArrayList<String>()
arList.addAll(listOf(1,2,3,4,5))

edited May 29, 2022 at 8:53

Peter Mortensen

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answered Oct 21, 2021 at 7:04

Abdulkerim Yıldırım

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Comments

Peter Mortensen · Accepted Answer · 2022-05-29 09:05:02Z

0

If you needed to add a lot of integers it'd probably be easiest to use a for loop. For example, adding 28 days to a daysInFebruary array.

ArrayList<Integer> daysInFebruary = new ArrayList<>();

for(int i = 1; i <= 28; i++) {
    daysInFebruary.add(i);
}

edited May 29, 2022 at 9:05

Peter Mortensen

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answered Oct 15, 2018 at 6:56

rhino9

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1 Comment

Peter Mortensen Over a year ago

Yes, for some of the examples in answers here. But otherwise not.

Peter Mortensen · Accepted Answer · 2022-05-29 08:51:38Z

-6

I believe scaevity's answer is incorrect. The proper way to initialize with multiple values would be this...

int[] otherList = {1,2,3,4,5};

So the full answer with the proper initialization would look like this

int[] otherList = {1,2,3,4,5};
arList.addAll(Arrays.asList(otherList));

edited May 29, 2022 at 8:51

Peter Mortensen

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answered Sep 27, 2013 at 0:47

user2821654

1

1 Comment

krispy Over a year ago

This does not compile because int is a primitive type and Arrays.asList() does not work correctly on arrays of primitive types. The chosen answer uses Integer, and that is the correct way to do it.

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