Do you know why this isn't working?

package com.codegym.task.task06.task0612;
/*
Calculator
*/
public class Calculator {
public static int plus(int a, int b) {
int sum = a + b;
return sum;
}
public static int minus(int a, int b) {
int sum = a - b;
return sum;
}
public static int multiply(int a, int b) {
int sum = a * b;
return sum;
}
public static double divide(int a, int b) {
double sum = a / b;
return sum;
}
public static double percent(int a, int b) {
double sum = (a * b) / 100;
return sum;
}
public static void main(String[] args) {
}
}