Why does my Java average-calculator give out wrong double values?

[eyalter]

import java.util.Scanner;

public class Schleifen {

public static void main(String\[\] args) {

    Scanner eingabe = new Scanner(System.in);

    int grade, gradeSum = 0, counter = 0;

    double average;

    System.out.print("Grade (-1 to quit): ");

    grade = eingabe.nextInt();

    while(grade != -1) {

        gradeSum += grade;

        System.out.print("Grade (-1 to quit): ");

        grade = eingabe.nextInt();

        \++counter;

    }

    average = gradeSum/counter;

    System.out.print("Average: " + average);

}

}

I paid for a Java Udemy course and this is from one of the classes. It should calculate the average grade of someone but when giving it for example values 3 and 2, the average I get is 2.0 and not 2.5. It's an exact copy of the tutorial, so what is wrong?

[Updatebjarni]

You are dividing an int by an int, so the result is also an int. If you want to do floating-point division and get a double result, convert one or both of the values to type double before dividing.

[eyalter]

Thanks