Question

Recently I came across an API and it was using some Parameter

void doSomething(final String... olah) {
}

I never have seen something like that.

I have a List<String> now and I want to call that function with my list of string. How can I achieve that?

Answer 1

Welcome to modern Java. That syntax is called varargs in Java.

http://docs.oracle.com/javase/1.5.0/docs/guide/language/varargs.html

You can think of it like

void doSomething(final String[] olaf) {

}

The only difference is that as the name suggests, it is Variable Length Arguments. You can invoke it with 0 to any number or arguments. Thus, doSomething("foo"), doSomething("foo", "bar"), doSomething("foo", "bar", "baz") are all supported.

In order to invoke this method with a List argument though, you’ll have to first convert the list into a String[].

Something like this will do:

List<String> myList; // Hope you're acquainted with generics?

doSomething(myList.toArray(new String[myList.size()]));