How to make a decision without an if statement

To avoid direct use of flow control statements like if or while you can use Math.min and Math.max. For this particular problem using a loop would not be efficient either.

They may technically use an if statements or the equivalent, but so do a lot of your other standard library calls you already make:

public static double pay (double salary, int hours) {
     int hoursWorkedRegularTime = Math.min(8, hours);
     int hoursWorkedOverTime = Math.max(0, hours - 8);
     return (hoursWorkedRegularTime * salary) +
            (hoursWorkedOverTime  * (salary * 1.5));
}