Using Math.round() in a method vs. directly

Question

I have this code here:

public class Main {

    public static void main(String[] args) {
        System.out.println(Math.round(12.5));
        System.out.println(round(12.5));
    }

    public static double round(double integer) {
        return Math.round(integer);
    }
}

When I run the code it outputs:

13
13.0

Why is it that when I run Math.round() normally inside the main method, it provides an integer value, while it provides a double value inside the "round" method? I know that my method is of type "double" but Java doesn't let me change it to "int." Any reason behind this? Thanks.

Answer 1

In the call to :

Math.round(12.5)

12.5 is evaluated as a double and the method, Math#round, with the following signature is called:

public static long round(double a)

because it returns a long it will print without any decimal place (i.e., 13). In the second print statement, however, you use:

public static double round(double integer) {
    return Math.round(integer);
}

which returns a double, hence the decimal value 13.0.