Variable scope and lifetime: Correct Solution

Given the following code:

public class Sciaca {
    private int or = 0;

    public void ilso(int na) {
        int toan = 0;
        A
        or += na;
        toan += na;
        ho += na;
        System.out.println("or=" + or + "  toan=" + toan + "  ho=" + ho);
    }

    public static void main(String[] args) {
        Sciaca s0 = new Sciaca();
        B
        Sciaca s1 = new Sciaca();
        s0.ilso(1);
        s0 = new Sciaca();
        s1.ilso(10);
        s0.ilso(100);
        s1 = s0;
        s1.ilso(1000);
        C
    }

    private static int ho = 0;
}
  1. What does the main method print?
  2. Which of the variables [ho, or, toan, s0, s1] are in scope at A ?
  3. Which are in scope at B ?
  4. Which are in scope at C ?

Solution

  1. Output:

    ho=1  or=1  toan=1
ho=10  or=10  toan=11
ho=100  or=100  toan=111
ho=1100  or=1000  toan=1111

  2. In scope at A : toan, ho, or

  3. In scope at B : toan, s0, s1

  4. In scope at C : toan

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

  1. toan is a static variable, ho is an instance variable, and or is a local variable.

  2. At A , s0 and s1 out of scope because they are local to the main method.

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

  4. At C , s0 and s1 are out of scope because they are not declared yet. ho is out of scope because it is an instance variable, but main is a static method. or is out of scope because it is local to ilso.

Related puzzles: