What is "T..." on Java?

Question

Looking at the methods of the Array class on libgdx. I found this method:

public void addAll (T... array) {
    addAll(array, 0, array.length);
}

I had never seen that "T..." before, and it turns out that it's incredibly hard to search for "T..." either on Google or here on Stack Overflow. I think I understand generics, but the "..." is new to me.

What does that mean? So, for example, if T is String, then how would I use this method? Why would I use it? And how would that be different from using "T[]" instead?

Answer 1

The T... is just a varargs parameter, where the element type happens to be T, the generic type parameter of the class.

The point is that you can call the method like this (assuming array is an Array<String>):

array.addAll("x", "y", "z");

which will be equivalent to

array.addAll(new String[] { "x", "y", "z" });

This can be used without generics too. For example:

public static int sum(int... elements) {
    int total = 0;
    for (int element : elements) {
        total += element;
    }
    return total;
}

Varargs parameters were introduced in Java 5.