(old thread, but just 2 cents as none mention Guava or other libs and some other details)
If You Can, Use Guava
It's worth pointing out the Guava way, which greatly simplifies these shenanigans:
Usage
For an Immutable List
Use the ImmutableList
class and its of()
and copyOf()
factory methods (elements can't be null):
List<String> il = ImmutableList.of("string", "elements"); // from varargs
List<String> il = ImmutableList.copyOf(aStringArray); // from array
For A Mutable List
Use the Lists
class and its newArrayList()
factory methods:
List<String> l1 = Lists.newArrayList(anotherListOrCollection); // from collection
List<String> l2 = Lists.newArrayList(aStringArray); // from array
List<String> l3 = Lists.newArrayList("or", "string", "elements"); // from varargs
Please also note the similar methods for other data structures in other classes, for instance in Sets
.
The main attraction could be to reduce the clutter due to generics for type-safety, as the use of the Guava factory methods allow the types to be inferred most of the time. However, this argument holds less water since Java 7 arrived with the new diamond operator.
But it's not the only reason (and Java 7 isn't everywhere yet): the shorthand syntax is also very handy, and the methods initializers, as seen above, allow to write more expressive code. You do in one Guava call what takes 2 with the current Java Collections.
If You Can't...
For an Immutable List
Use the JDK's Arrays
class and its asList()
factory method:
List<String> l1 = Arrays.asList(anArrayOfElements);
List<String> l2 = Arrays.asList("element1", "element2");
Note that the returned type for asList()
says ArrayList
, but it's not java.util.ArrayList
. It's an inner type, which copies ArrayList but actually directly references the past array and forbis modifications. See the next step if you need a mutable list.
For a Mutable List
Same as above, but wrapped with an actual java.util.ArrayList
:
List<String> l1 = new ArrayList<String>(Arrays.asList(array)); // Java 1.5 to 1.6
List<String> l1b = new ArrayList<>(Arrays.asList(array)); // Java 1.7+
List<String> l2 = new ArrayList<String>(Arrays.asList("a", "b")); // Java 1.5 to 1.6
List<String> l2b = new ArrayList<>(Arrays.asList("a", "b")); // Java 1.7+
For Educational Purposes: The Good ol' Manual Way
// for Java 1.5+
static <T> List<T> arrayToList(final T[] array) {
final List<String> l = new ArrayList<String>(array.length);
for (final String s : array) {
l.add(s);
}
return (l);
}
// for Java < 1.5 (no generics, no compile-time type-safety, boo!)
static List arrayToList(final Object[] array) {
final List l = new ArrayList(array.length);
for (int i = 0; i < array.length; i++) {
l.add(array[i]);
}
return (l);
}