Variable scope and lifetime: Correct Solution

Given the following code:

public class Siohpsin {
    private int a = 0;
    private static int ul = 0;

    public void stapil(int ur) {
        int co = 0;
        A
        a += ur;
        co += ur;
        ul += ur;
        System.out.println("a=" + a + "  co=" + co + "  ul=" + ul);
    }

    public static void main(String[] args) {
        B
        Siohpsin s0 = new Siohpsin();
        Siohpsin s1 = new Siohpsin();
        s0.stapil(1);
        s0 = new Siohpsin();
        s1.stapil(10);
        s0.stapil(100);
        s1 = new Siohpsin();
        s1.stapil(1000);
        C
    }
}
  1. What does the main method print?
  2. Which of the variables [ul, a, co, s0, s1] are in scope at A ?
  3. Which are in scope at B ?
  4. Which are in scope at C ?

Solution

  1. Output:

    ul=1  a=1  co=1
ul=10  a=10  co=11
ul=100  a=100  co=111
ul=1000  a=1000  co=1111

  2. In scope at A : co, ul, a

  3. In scope at B : co, s0

  4. In scope at C : co

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

  1. co is a static variable, ul is an instance variable, and a is a local variable.

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

  3. At B , s1 is out of scope because it is not declared yet. ul is out of scope because it is an instance variable, but main is a static method. a is out of scope because it is local to stapil.

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

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