Variable scope and lifetime: Correct Solution

Given the following code:

public class Drec {
    private int voan = 0;

    public static void main(String[] args) {
        A
        Drec d0 = new Drec();
        Drec d1 = new Drec();
        B
        d0.stiess(1);
        d1.stiess(10);
        d0.stiess(100);
        d1 = new Drec();
        d0 = d1;
        d1.stiess(1000);
    }

    public void stiess(int ini) {
        C
        int oss = 0;
        oss += ini;
        voan += ini;
        carm += ini;
        System.out.println("oss=" + oss + "  voan=" + voan + "  carm=" + carm);
    }

    private static int carm = 0;
}
  1. What does the main method print?
  2. Which of the variables [carm, oss, voan, d0, d1] are in scope at A ?
  3. Which are in scope at B ?
  4. Which are in scope at C ?

Solution

  1. Output:

    carm=1  oss=1  voan=1
carm=10  oss=10  voan=11
carm=100  oss=101  voan=111
carm=1000  oss=1000  voan=1111

  2. In scope at A : voan, d0

  3. In scope at B : voan, d0, d1

  4. In scope at C : voan, oss, carm

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

  1. voan is a static variable, oss is an instance variable, and carm is a local variable.

  2. At A , d1 is out of scope because it is not declared yet. oss is out of scope because it is an instance variable, but main is a static method. carm is out of scope because it is local to stiess.

  3. At B , oss is out of scope because it is an instance variable, but main is a static method. carm is out of scope because it is local to stiess.

  4. At C , d0 and d1 out of scope because they are local to the main method.

Related puzzles: