Variable scope and lifetime: Correct Solution

Given the following code:

public class Ioiss {
    public static void main(String[] args) {
        A
        Ioiss i0 = new Ioiss();
        Ioiss i1 = new Ioiss();
        i0.popan(1);
        i1.popan(10);
        i1 = i0;
        i0.popan(100);
        i0 = new Ioiss();
        i1.popan(1000);
        B
    }

    private static int iwn = 0;

    public void popan(int sath) {
        C
        int os = 0;
        os += sath;
        iwn += sath;
        ia += sath;
        System.out.println("os=" + os + "  iwn=" + iwn + "  ia=" + ia);
    }

    private int ia = 0;
}
  1. What does the main method print?
  2. Which of the variables [ia, os, iwn, i0, i1] are in scope at A ?
  3. Which are in scope at B ?
  4. Which are in scope at C ?

Solution

  1. Output:

    ia=1  os=1  iwn=1
ia=10  os=11  iwn=10
ia=100  os=111  iwn=101
ia=1000  os=1111  iwn=1101

  2. In scope at A : os, i0

  3. In scope at B : os

  4. In scope at C : os, iwn, ia

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

  1. os is a static variable, iwn is an instance variable, and ia is a local variable.

  2. At A , i1 is out of scope because it is not declared yet. iwn is out of scope because it is an instance variable, but main is a static method. ia is out of scope because it is local to popan.

  3. At B , i0 and i1 are out of scope because they are not declared yet. iwn is out of scope because it is an instance variable, but main is a static method. ia is out of scope because it is local to popan.

  4. At C , i0 and i1 out of scope because they are local to the main method.

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