How to quickly and conveniently create a one element arraylist

2018-06-09 05:21:11

This question already has an answer here:

Initialization of an ArrayList in one line 32 answers

The easiest way, that I know of, is to create a fixed-size single element List with Arrays.asList(T...) like

// Returns a List backed by a varargs T.
return Arrays.asList(s);

If it needs vary in size you can construct an ArrayList and the fixed-size List like

return new ArrayList<String>(Arrays.asList(s));

and (in Java 7+) you can use the diamond operator <> to make it

return new ArrayList<>(Arrays.asList(s));

Collections.singletonList(object)

You can use the utility method Arrays.asList and feed that result into a new ArrayList .

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

Other options:

List<String> list = new ArrayList<String>(Collections.nCopies(1, s));

and

List<String> list = new ArrayList<String>(Collections.singletonList(s));

ArrayList(Collection) constructor.

Arrays.asList method.

Collections.nCopies method.

Collections.singletonList method.

With Java 7+, you may use the "diamond operator", replacing new ArrayList<String>(...) with new ArrayList<>(...) .

Java 9

If you're using Java 9+, you can use the List.of method:

List<String> list = new ArrayList<>(List.of(s));

Regardless of the use of each option above, you may choose not to use the new ArrayList<>() wrapper if you don't need your list to be mutable.

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