Initializing an ArrayList with an array in a single line

Question

I have an array of Strings and I'm looking to be able to do something along the lines of

String[] arrayOfStrings = {"this", "is", "an", "array", "of", "strings"};
List<String> listOfStrings = new ArrayList<String>( arrayOfStrings );

or

List<String> listOfStrings = new ArrayList<String>();
listOfStrings.addAll( arrayOfStrings );

I know I can do both of these if my strings are already in a collection, and also that I can iterate through the array and add them individually, but that one's a little bit messy.

Is there any way to initialise a List (or any collection for that matter) with an array?

Rohit Jain · Accepted Answer · 2013-02-07T21:57:36.243

10

You can use Arrays.asList method, which takes a var-args, and returns a fixed-size List backed by an array. So, you can't add any element to this list. Further, any modification done to the elements of the List will be reflected back in the array.

String[] arrayOfStrings = {"this", "is", "an", "array", "of", "strings"};
List<String> list = Arrays.asList(arrayOfStrings);

or: -

List<String> list = Arrays.asList("this", "is", "an", "array", "of", "strings");

If you want to increase the size of this list, you would have to pass it in ArrayList constructor.

List<String> list = new ArrayList<String>(Arrays.asList(arrayOfStrings));

edited Feb 07 '13 at 21:57

answered Feb 07 '13 at 21:49

Rohit Jain

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Is the list `unmodifiable`?You mean you can not add elements.The list contents are modifiable – Cratylus Feb 07 '13 at 21:58
@Cratylus. Yeah, I mean we cannot add any element in that. I'll update the answer to remove confusion. – Rohit Jain Feb 07 '13 at 21:59

score 3 · Answer 2 · answered Feb 07 '13 at 21:49

3

You could use Arrays.asList() static method.

For example:

String[] arrayOfStrings = {"this", "is", "an", "array", "of", "strings"};
List<String> list = Arrays.asList(arrayOfStrings);

Note, that you create a fixed-size list "backed up by array" in such a way. If you want to be able to expand it, you'll have to do the following way:

String[] arrayOfStrings = {"this", "is", "an", "array", "of", "strings"};
List<String> list = new ArrayList<String>(Arrays.asList(arrayOfStrings));

answered Feb 07 '13 at 21:49

Andrew Logvinov

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Note that it creates a fixed-size list, so if you specifically want an `ArrayList` you need to do `new ArrayList(Arrays.asList("a", "b", "c"))`. – Russell Zahniser Feb 07 '13 at 21:50
@RussellZahniser That's a valid note. I'll add this to the answer. – Andrew Logvinov Feb 07 '13 at 21:50

score 1 · Answer 3 · answered Feb 07 '13 at 21:49

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You can use asList()

Arrays.asList(T... a) Returns a fixed-size list backed by the specified array.

http://docs.oracle.com/javase/6/docs/api/java/util/Arrays.html

answered Feb 07 '13 at 21:49

John Humphreys

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score 1 · Answer 4 · answered Feb 07 '13 at 21:53

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This may not fall exactly in your question, but may be worth a consideration.

List<String> list = Arrays.asList("this", "is", "an", "array", "of", "strings");

answered Feb 07 '13 at 21:53

Bernhard Barker

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score 0 · Answer 5 · answered Oct 05 '20 at 20:23

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ArrayList<List<String>> arrayStringMega = new ArrayList<List<String>>(Arrays.asList(Arrays.asList("1","2","3"),Arrays.asList("2","3","4")));

answered Oct 05 '20 at 20:23

Supun Sandeeptha

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It's just another duplicate answer about `Arrays.asList` – Nowhere Man Oct 06 '20 at 01:15
If you take a closer look. It's been done in one line :) – Supun Sandeeptha Oct 06 '20 at 01:57

Initializing an ArrayList with an array in a single line

5 Answers5