Variable scope and lifetime: Correct Solution

Given the following code:

public class JolDro {
    private static int puc = 0;
    private int spe = 0;

    public static void main(String[] args) {
        JolDro j0 = new JolDro();
        A
        JolDro j1 = new JolDro();
        j0.irdrot(1);
        j0 = new JolDro();
        j1.irdrot(10);
        j1 = j0;
        j0.irdrot(100);
        j1.irdrot(1000);
        B
    }

    public void irdrot(int pei) {
        int os = 0;
        C
        puc += pei;
        spe += pei;
        os += pei;
        System.out.println("puc=" + puc + "  spe=" + spe + "  os=" + os);
    }
}
  1. What does the main method print?
  2. Which of the variables [os, puc, spe, j0, j1] are in scope at A ?
  3. Which are in scope at B ?
  4. Which are in scope at C ?

Solution

  1. Output:

    os=1  puc=1  spe=1
os=11  puc=10  spe=10
os=111  puc=100  spe=100
os=1111  puc=1100  spe=1000

  2. In scope at A : os, j0, j1

  3. In scope at B : os

  4. In scope at C : os, puc, spe

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

  1. os is a static variable, puc is an instance variable, and spe is a local variable.

  2. At A , puc is out of scope because it is an instance variable, but main is a static method. spe is out of scope because it is local to irdrot.

  3. At B , j0 and j1 are out of scope because they are not declared yet. puc is out of scope because it is an instance variable, but main is a static method. spe is out of scope because it is local to irdrot.

  4. At C , j0 and j1 out of scope because they are local to the main method.

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