Variable scope and lifetime: Correct Solution

Given the following code:

public class Ress {
    private int acal = 0;

    public static void main(String[] args) {
        A
        Ress r0 = new Ress();
        Ress r1 = new Ress();
        B
        r0.eckWheos(1);
        r0 = r1;
        r1.eckWheos(10);
        r0.eckWheos(100);
        r1 = r0;
        r1.eckWheos(1000);
    }

    private static int imin = 0;

    public void eckWheos(int o) {
        int al = 0;
        imin += o;
        al += o;
        acal += o;
        System.out.println("imin=" + imin + "  al=" + al + "  acal=" + acal);
        C
    }
}
  1. What does the main method print?
  2. Which of the variables [acal, imin, al, r0, r1] are in scope at A ?
  3. Which are in scope at B ?
  4. Which are in scope at C ?

Solution

  1. Output:

    acal=1  imin=1  al=1
acal=11  imin=10  al=10
acal=111  imin=100  al=110
acal=1111  imin=1000  al=1110

  2. In scope at A : acal, r0

  3. In scope at B : acal, r0, r1

  4. In scope at C : acal, al

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

  1. acal is a static variable, al is an instance variable, and imin is a local variable.

  2. At A , r1 is out of scope because it is not declared yet. al is out of scope because it is an instance variable, but main is a static method. imin is out of scope because it is local to eckWheos.

  3. At B , al is out of scope because it is an instance variable, but main is a static method. imin is out of scope because it is local to eckWheos.

  4. At C , imin is out of scope because it is not declared yet. r0 and r1 out of scope because they are local to the main method.

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