Variable scope and lifetime: Correct Solution

Given the following code:

public class SteGeine {
    public void huin(int o) {
        int io = 0;
        io += o;
        el += o;
        a += o;
        System.out.println("io=" + io + "  el=" + el + "  a=" + a);
        A
    }

    private int el = 0;
    private static int a = 0;

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

Solution

  1. Output:

    a=1  io=1  el=1
a=10  io=10  el=11
a=100  io=100  el=111
a=1000  io=1001  el=1111

  2. In scope at A : el, io

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

  4. In scope at C : el, s0, s1

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

  1. el is a static variable, io is an instance variable, and a is a local variable.

  2. At A , a is out of scope because it is not declared yet. s0 and s1 out of scope because they are local to the main method.

  3. At B , io 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 huin.

  4. At C , io 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 huin.

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