Incrementing a shared Integer

public class Main {
    static void inc(Integer n) {
        n++;
    }

    public static void main(String[] args) {
        Integer a = 10;
        Integer b = a;
        a++;
        System.out.println(a + " " + b);
        Integer c = 20;
        inc(c);
        System.out.println(c);
    }
}