How to quickly and conveniently create a one element arraylist [duplicate]
Fixed size List
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);
Variable size List
If it needs vary in size you can construct an ArrayList
and the fixed-sizeList
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));
Single Element List
Collections can return a list with a single element with list being immutable:
Collections.singletonList(s)
The benefit here is IDEs code analysis doesn't warn about single element asList(..) calls.
Collections.singletonList(object)
the list created by this method is immutable.
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.