Variable scope and lifetime: Correct Solution

Given the following code:

public class Fethan {
    private int tred = 0;

    public static void main(String[] args) {
        A
        Fethan f0 = new Fethan();
        Fethan f1 = new Fethan();
        B
        f0.tesLanta(1);
        f0 = f1;
        f1.tesLanta(10);
        f1 = f0;
        f0.tesLanta(100);
        f1.tesLanta(1000);
    }

    public void tesLanta(int u) {
        C
        int mi = 0;
        mi += u;
        tred += u;
        ru += u;
        System.out.println("mi=" + mi + "  tred=" + tred + "  ru=" + ru);
    }

    private static int ru = 0;
}
  1. What does the main method print?
  2. Which of the variables [ru, mi, tred, f0, f1] are in scope at A ?
  3. Which are in scope at B ?
  4. Which are in scope at C ?

Solution

  1. Output:

    ru=1  mi=1  tred=1
ru=10  mi=10  tred=11
ru=100  mi=110  tred=111
ru=1000  mi=1110  tred=1111

  2. In scope at A : tred, f0

  3. In scope at B : tred, f0, f1

  4. In scope at C : tred, mi, ru

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

  1. tred is a static variable, mi is an instance variable, and ru is a local variable.

  2. At A , f1 is out of scope because it is not declared yet. mi is out of scope because it is an instance variable, but main is a static method. ru is out of scope because it is local to tesLanta.

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

  4. At C , f0 and f1 out of scope because they are local to the main method.

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