Does .asSet(...) exist in any API?

Question

I'm looking for a very simple way to create a Set.

Arrays.asList("a", "b" ...) creates a List<String>

Is there anything similar for Set ?

Answer 1

Now with Java 8 you can do this without need of third-party framework:

Set<String> set = Stream.of("a","b","c").collect(Collectors.toSet());

See Collectors.

Enjoy!

Answer 2

Using Guava, it is as simple as that:

Set<String> mySet = ImmutableSet.<String> of("a", "b");

Or for a mutable set:

Set<String> mySet = Sets.newHashSet("a", "b")

For more data types see the Guava user guide

Answer 3

You could use

new HashSet<String>(Arrays.asList("a","b"));

Answer 4

In Java 9, similar function has been added via factory methods:

Set<String> oneLinerSet = Set.of("a", "b", ...);

(There are equivalents for List as well.)

Answer 5

For the special cases of sets with zero or one members, you can use:

java.util.Collections.EMPTY_SET

and:

java.util.Collections.singleton("A")

Answer 6

As others have said, use:

new HashSet<String>(Arrays.asList("a","b"));

The reason this does not exist in Java is that Arrays.asList returns a fixed sized list, in other words:

public static void main(String a[])
{
  List<String> myList = Arrays.asList("a", "b");
  myList.add("c");
}

Returns:

Exception in thread "main" java.lang.UnsupportedOperationException
    at java.util.AbstractList.add(Unknown Source)
    at java.util.AbstractList.add(Unknown Source)

There is no JDK implementation of a "fixed-size" Set inside the Arrays class. Why do you want this? A Set guarantees that there are no duplicates, but if you are typing them out by hand, you shouldn't need that functionality... and List has more methods. Both interfaces extend Collection and Iterable.

---

As others have said, use guava If you really want this functionality - since it's not in the JDK. Look at their answers (in particular Michael Schmeißer's answer) for information on that.

Answer 7

No but you can do it like this

new HashSet<String>(Arrays.asList("a", "b", ...));

Answer 8

Here's a little method you can use

  /**
   * Utility method analogous to {@link java.util.Arrays#asList(Object[])}
   *
   * @param ts
   * @param <T>
   * @return the set of all the parameters given.
   */
  @SafeVarargs
  @SuppressWarnings("varargs")
  public static <T> Set<T> asSet(T... ts) {
    return new HashSet<>(Arrays.asList(ts));
  }

Answer 9

In guava you could use

Set<String> set = Sets.newHashSet("a","b","c");

newHashSet

Answer 10

Another way to do it using Java 8 and enums would be:

Set<String> set = EnumSet.of(StandardOpenOption.CREATE, StandardOpenOption.READ);

See EnumSet.

I would recommend a performance analysis between this approach and

Set<String> set = Stream.of(StandardOpenOption.CREATE, StandardOpenOption.READ).collect(Collectors.toSet());

because if you have more than five elements the javadoc of the method states that may be performance issues as you can see in the javadoc of Set.Of(E, E...).

Answer 11

List<String> myList = new ArrayList<String>(Arrays.asList("a", "b"));
myList.add("c");
System.out.println(myList);

It worked without error