Variable scope and lifetime: Correct Solution

Given the following code:

public class Itro {
    private static int tro = 0;

    public void insic(int seng) {
        int e = 0;
        A
        tro += seng;
        e += seng;
        scia += seng;
        System.out.println("tro=" + tro + "  e=" + e + "  scia=" + scia);
    }

    private int scia = 0;

    public static void main(String[] args) {
        B
        Itro i0 = new Itro();
        Itro i1 = new Itro();
        C
        i0.insic(1);
        i1.insic(10);
        i0.insic(100);
        i0 = i1;
        i1 = new Itro();
        i1.insic(1000);
    }
}
  1. What does the main method print?
  2. Which of the variables [scia, tro, e, i0, i1] are in scope at A ?
  3. Which are in scope at B ?
  4. Which are in scope at C ?

Solution

  1. Output:

    scia=1  tro=1  e=1
scia=11  tro=10  e=10
scia=111  tro=100  e=101
scia=1111  tro=1000  e=1000

  2. In scope at A : scia, e, tro

  3. In scope at B : scia, i0

  4. In scope at C : scia, i0, i1

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

  1. scia is a static variable, e is an instance variable, and tro is a local variable.

  2. At A , i0 and i1 out of scope because they are local to the main method.

  3. At B , i1 is out of scope because it is not declared yet. e is out of scope because it is an instance variable, but main is a static method. tro is out of scope because it is local to insic.

  4. At C , e is out of scope because it is an instance variable, but main is a static method. tro is out of scope because it is local to insic.

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