Variable scope and lifetime: Correct Solution

Given the following code:

public class Ninrics {
    private int hi = 0;

    public static void main(String[] args) {
        Ninrics n0 = new Ninrics();
        A
        Ninrics n1 = new Ninrics();
        n0.pobrel(1);
        n1.pobrel(10);
        n1 = n0;
        n0 = new Ninrics();
        n0.pobrel(100);
        n1.pobrel(1000);
        B
    }

    public void pobrel(int rhad) {
        int sa = 0;
        sa += rhad;
        hi += rhad;
        su += rhad;
        System.out.println("sa=" + sa + "  hi=" + hi + "  su=" + su);
        C
    }

    private static int su = 0;
}
  1. What does the main method print?
  2. Which of the variables [su, sa, hi, n0, n1] are in scope at A ?
  3. Which are in scope at B ?
  4. Which are in scope at C ?

Solution

  1. Output:

    su=1  sa=1  hi=1
su=10  sa=10  hi=11
su=100  sa=100  hi=111
su=1000  sa=1001  hi=1111

  2. In scope at A : hi, n0, n1

  3. In scope at B : hi

  4. In scope at C : hi, sa

Explanation (which you do not need to write out in your submitted solution):

  1. hi is a static variable, sa is an instance variable, and su is a local variable.

  2. At A , sa is out of scope because it is an instance variable, but main is a static method. su is out of scope because it is local to pobrel.

  3. At B , n0 and n1 are out of scope because they are not declared yet. sa is out of scope because it is an instance variable, but main is a static method. su is out of scope because it is local to pobrel.

  4. At C , su is out of scope because it is not declared yet. n0 and n1 out of scope because they are local to the main method.

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