Variable scope and lifetime: Correct Solution

Given the following code:

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

    private int id = 0;

    public void duis(int sa) {
        int oss = 0;
        id += sa;
        oss += sa;
        ra += sa;
        System.out.println("id=" + id + "  oss=" + oss + "  ra=" + ra);
        C
    }

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

Solution

  1. Output:

    ra=1  id=1  oss=1
ra=10  id=10  oss=11
ra=110  id=100  oss=111
ra=1110  id=1000  oss=1111

  2. In scope at A : oss, p0, p1

  3. In scope at B : oss, p0, p1

  4. In scope at C : oss, ra

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

  1. oss is a static variable, ra is an instance variable, and id is a local variable.

  2. At A , ra is out of scope because it is an instance variable, but main is a static method. id is out of scope because it is local to duis.

  3. At B , ra is out of scope because it is an instance variable, but main is a static method. id is out of scope because it is local to duis.

  4. At C , id 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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