Variable scope and lifetime: Correct Solution

Given the following code:

public class Stross {
    private static int prar = 0;

    public static void main(String[] args) {
        Stross s0 = new Stross();
        A
        Stross s1 = new Stross();
        B
        s0.omtrad(1);
        s0 = s1;
        s1.omtrad(10);
        s1 = s0;
        s0.omtrad(100);
        s1.omtrad(1000);
    }

    public void omtrad(int mosm) {
        int sqos = 0;
        spo += mosm;
        prar += mosm;
        sqos += mosm;
        System.out.println("spo=" + spo + "  prar=" + prar + "  sqos=" + sqos);
        C
    }

    private int spo = 0;
}
  1. What does the main method print?
  2. Which of the variables [sqos, spo, prar, s0, s1] are in scope at A ?
  3. Which are in scope at B ?
  4. Which are in scope at C ?

Solution

  1. Output:

    sqos=1  spo=1  prar=1
sqos=10  spo=11  prar=10
sqos=110  spo=111  prar=100
sqos=1110  spo=1111  prar=1000

  2. In scope at A : spo, s0, s1

  3. In scope at B : spo, s0, s1

  4. In scope at C : spo, sqos

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

  1. spo is a static variable, sqos is an instance variable, and prar is a local variable.

  2. At A , sqos is out of scope because it is an instance variable, but main is a static method. prar is out of scope because it is local to omtrad.

  3. At B , sqos is out of scope because it is an instance variable, but main is a static method. prar is out of scope because it is local to omtrad.

  4. At C , prar is out of scope because it is not declared yet. s0 and s1 out of scope because they are local to the main method.

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