Question

class smth{
    public static void main(String[] args){
        private Integer x = new Integer(17);
        inc(x);
        System.out.print("x="+x);
    }
    public static void inc(Integer x){
        x++;
        System.out.println("n="+x);
    }
}

output:
n=18;
x=17;

Integer is an object and I don’t understand why the value of x did not change in this case.

Answer 1

Cause Integer is immutable object. When you send it to method, new reference to it is created. When you do increment, reference inside method is reassigned to new Integer with value 18 but reference inside main is still referencing to old Integer with value 17.