What do three dots (...) mean in java and how are they used?

It stands for varargs and is used to pass 0 or more parameters of the same type. For example, the method you indicate:

public void metodoX(int ... args) {
}

Supports that you can pass 0, 1 or more type arguments intonly.

varargs can only be used as the last type of parameter to use in a method. For example:

public void metodoX(String mensaje, int ... args) { }

It means that the first argument must be a Stringand the others (0, 1 or more) are of type int.

In case you put a varargs type variable, no variable definition can go after this. Example:

//error de compilación
public void metodoX(int ... args, String s) { }

Java interprets varargs parameters as an array. For example, an implementation for the method would be:

public void metodoX(int ... args) {
    for (int numero : args {
        System.out.print(numero + " ");
    }
    System.out.println();
}

Therefore, it also supports that instead of sending multiple arguments, you can send an array instead. Example:

metodoX(1, 2, 3);
metodoX(new int[] { 1, 2, 3 });

Departure:

1 2 3
1 2 3

Important : Keep in mind that if you have the method overloaded, the method that varargs uses will be the last option the compiler chooses to check your code, just as it will be the last option the JVM uses in case you call one of the overloaded methods.

Example:

public void metodoX(int x) {
    System.out.println("MetodoX con un argumento");
}

public void metodoX(int x, int y) {
    System.out.println("MetodoX con dos argumentos");
}

public void metodoX(int ... args) {
    System.out.println("MetodoX con varargs");
}

//...

metodoX(10);
metodoX(10, 20);
metodoX(10, 20, 30);

Departure:

MetodoX con un argumento
MetodoX con dos argumentos
MetodoX con varargs

It means that it is an argument variable, it is similar to an array ( [] ) and it supports sending 0 or more parameters separated by a comma (,)

Example :

//version de metodo main con arreglo comun
public static void main (String [] args)
{
    metodo(1,2,3,4,5,6,7,8,9,10); // [ 1  2  3  4  5  6  7  8  9  10 ]
    metodo(); //sin argumentos
}

//version de metodo main con una variable de argumentos
publc static void main (String ... args)
{
    metodo(1,2,3,4,5,6,7,8,9,10); // [ 1  2  3  4  5  6  7  8  9  10 ]
    metodo(); //sin argumentos
}


public static void metodo(int ... argumentos)
{
    if(argumentos.length > 0)
    {
        for(int pivote : argumentos)
        {
            System.out.println(pivote);
        }
    }
    else
    {
        System.out.println("sin argumentos");
    }
}

I hope it helps you

Greetings.