EnumSet from array, shortest variant?

Question

I need an EnumSet from an array (which is given through a varargs method parameter). First, I was surprised that there is no varargs constructor method in EnumSet (there is EnumSet#of(E first, E... rest)). As a workaround, I used the following variant:

EnumSet<Options> temp = EnumSet.copyOf(Arrays.asList(options));

However, this triggers a java.lang.IllegalArgumentException: Collection is empty. So, now I ended up with the following, which looks somewhat ridiculous:

EnumSet<Options> temp = options.length > 0 ? 
                        EnumSet.copyOf(Arrays.asList(options)) : 
                        EnumSet.noneOf(Options.class);

If course this could be moved to some utility method, but still, I'm asking myself if there is a simpler way using existing methods?

Answer 1

Just an alternative. Same amount of code, except no need converting to list, using EnumSet.of() :

EnumSet<Options> temp = options.length > 0 ? 
                        EnumSet.of(options[0], options) : 
                        EnumSet.noneOf(Options.class);

No worries that first element is repeated(it won't be duplicated in a set anyway), no performance gain or penalties as well.

Answer 2

This is two lines, but slightly less complex:

EnumSet<Options> temp = EnumSet.noneOf(Options.class); // make an empty enumset
temp.addAll(Arrays.asList(options)); // add varargs to it

I don't consider this worse than any other kind of variable declaration for a class which doesn't have the constructor you want:

    SomeClass variable = new SomeClass(); // make an empty object
    variable.addStuff(stuff); // add stuff to it

Answer 3

Guava has factory methods for these kinds of situations: It still needs the call to Arrays.asList but at least it's readable.

import com.google.common.collect.Sets;

EnumSet<Options> temp = Sets.newEnumSet(Arrays.asList(options), Options.class);