为什么这个if语句不返回布尔值？

Question

I am trying to make a program that will show if an input is a perfect number meaning the factors (not including the number) add up to be the same as that number. I got it working other than the return value. I want to return true if the sum of the factors is equal to the number entered however it just won't do it.

I have tried moving the if statement all over the code and it doesn't work anywhere.

public class Main {

public static void main(String[] args) {
    isPerfectNumber(28);
}

public static boolean isPerfectNumber(int number) {
    if (number < 1) {
        return false;
    }
    int numberToTest = 1;
    int sumOfFactors = 0;

    while (numberToTest < number) {
        if (number % numberToTest == 0) {
            sumOfFactors += numberToTest;
        }
        numberToTest++;
    }

    if (sumOfFactors == number) {
        return true;
    }else{
        return false;
    }
}

}

I expect that when the code see that the sumOfFactors will have the sum = to the number entered and that's when I get the true statement however when that happens it doesn't return​ true. In fact, it doesn't return anything and states that the method returns were not used.

Answer 1

It "isn't working" because you aren't printing the result.

public static void main(String[] args) {
    isPerfectNumber(28);
}

should be

public static void main(String[] args) {
    System.out.println(isPerfectNumber(28));
}

which is "true". Also,

if (sumOfFactors == number) {
    return true;
} else {
    return false;
}

is a long way to write

return sumOfFactors == number;

And, if you're using Java 8+, your isPerfectNumber method can be written as a one-liner with an IntStream and a lambda filter like

public static boolean isPerfectNumber(int number) {
    return number >= 1 && IntStream //
            .range(1, number) //
            .filter(i -> number % i == 0) //
            .sum() == number;
}