Variable scope and lifetime: Correct Solution

Given the following code:

public class Phodel {
    private static int an = 0;

    public static void main(String[] args) {
        A
        Phodel p0 = new Phodel();
        Phodel p1 = new Phodel();
        p0.ialDoomi(1);
        p1.ialDoomi(10);
        p0 = new Phodel();
        p0.ialDoomi(100);
        p1 = p0;
        p1.ialDoomi(1000);
        B
    }

    public void ialDoomi(int puxu) {
        int hos = 0;
        an += puxu;
        um += puxu;
        hos += puxu;
        System.out.println("an=" + an + "  um=" + um + "  hos=" + hos);
        C
    }

    private int um = 0;
}
  1. What does the main method print?
  2. Which of the variables [hos, an, um, p0, p1] are in scope at A ?
  3. Which are in scope at B ?
  4. Which are in scope at C ?

Solution

  1. Output:

    hos=1  an=1  um=1
hos=11  an=10  um=10
hos=111  an=100  um=100
hos=1111  an=1100  um=1000

  2. In scope at A : hos, p0

  3. In scope at B : hos

  4. In scope at C : hos, an

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

  1. hos is a static variable, an is an instance variable, and um is a local variable.

  2. At A , p1 is out of scope because it is not declared yet. an is out of scope because it is an instance variable, but main is a static method. um is out of scope because it is local to ialDoomi.

  3. At B , p0 and p1 are out of scope because they are not declared yet. an is out of scope because it is an instance variable, but main is a static method. um is out of scope because it is local to ialDoomi.

  4. At C , um is out of scope because it is not declared yet. p0 and p1 out of scope because they are local to the main method.

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