Variable scope and lifetime: Correct Solution

Given the following code:

public class Mion {
    public static void main(String[] args) {
        A
        Mion m0 = new Mion();
        Mion m1 = new Mion();
        m0.anor(1);
        m0 = m1;
        m1 = m0;
        m1.anor(10);
        m0.anor(100);
        m1.anor(1000);
        B
    }

    private static int espa = 0;

    public void anor(int pri) {
        C
        int al = 0;
        aw += pri;
        al += pri;
        espa += pri;
        System.out.println("aw=" + aw + "  al=" + al + "  espa=" + espa);
    }

    private int aw = 0;
}
  1. What does the main method print?
  2. Which of the variables [espa, aw, al, m0, m1] are in scope at A ?
  3. Which are in scope at B ?
  4. Which are in scope at C ?

Solution

  1. Output:

    espa=1  aw=1  al=1
espa=10  aw=10  al=11
espa=110  aw=100  al=111
espa=1110  aw=1000  al=1111

  2. In scope at A : al, m0

  3. In scope at B : al

  4. In scope at C : al, espa, aw

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

  1. al is a static variable, espa is an instance variable, and aw is a local variable.

  2. At A , m1 is out of scope because it is not declared yet. espa is out of scope because it is an instance variable, but main is a static method. aw is out of scope because it is local to anor.

  3. At B , m0 and m1 are out of scope because they are not declared yet. espa is out of scope because it is an instance variable, but main is a static method. aw is out of scope because it is local to anor.

  4. At C , m0 and m1 out of scope because they are local to the main method.

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