Variable scope and lifetime: Correct Solution

Given the following code:

public class Talm {
    public static void main(String[] args) {
        Talm t0 = new Talm();
        A
        Talm t1 = new Talm();
        B
        t0.polin(1);
        t0 = new Talm();
        t1 = t0;
        t1.polin(10);
        t0.polin(100);
        t1.polin(1000);
    }

    private static int to = 0;
    private int piw = 0;

    public void polin(int ar) {
        int is = 0;
        piw += ar;
        to += ar;
        is += ar;
        System.out.println("piw=" + piw + "  to=" + to + "  is=" + is);
        C
    }
}
  1. What does the main method print?
  2. Which of the variables [is, piw, to, t0, t1] are in scope at A ?
  3. Which are in scope at B ?
  4. Which are in scope at C ?

Solution

  1. Output:

    is=1  piw=1  to=1
is=10  piw=11  to=10
is=110  piw=111  to=100
is=1110  piw=1111  to=1000

  2. In scope at A : piw, t0, t1

  3. In scope at B : piw, t0, t1

  4. In scope at C : piw, is

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

  1. piw is a static variable, is is an instance variable, and to is a local variable.

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

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

  4. At C , to is out of scope because it is not declared yet. t0 and t1 out of scope because they are local to the main method.

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