Java – How to initialize HashSet values by construction


I need to create a Set with initial values.

Set<String> h = new HashSet<String>();

Is there a way to do this in one line of code? For instance, it's useful for a final static field.

Best Solution

There is a shorthand that I use that is not very time efficient, but fits on a single line:

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

Again, this is not time efficient since you are constructing an array, converting to a list and using that list to create a set.

When initializing static final sets I usually write it like this:

public static final String[] SET_VALUES = new String[] { "a", "b" };
public static final Set<String> MY_SET = new HashSet<>(Arrays.asList(SET_VALUES));

Slightly less ugly and efficiency does not matter for the static initialization.