Java Pass By Value/Reference check

class Student {
    String name;
    int roll;

    @Override
    public String toString() {
        return "Student [name=" + name + ", roll=" + roll + "]";
    }
}

class Helper {
    Student s;
    int x;

    Helper(Student s, int x) {
        this.s = s;
        this.x = x;
    }

    void change() {
        x = 999999;
        s.name = "Unknown";
        s.roll = 999999;
    }
}

public class PBVPBRTest {

    public static void change(Student s) {
        s.name = "Kune";
        s.roll = 962349;
    }

    public static void main(String[] args) {
        int x = 12;
        Student s = new Student();
        s.name = "Mohith";
        s.roll = 411641;

//      change(s);
        Helper h = new Helper(s, x);
        h.change();

        System.out.println(s);
        System.out.println(x + "");

    }
}