Variable scope and lifetime: Correct Solution

Given the following code:

public class Staustqing {
    private int oo = 0;
    private static int mo = 0;

    public void ealCactre(int ae) {
        A
        int de = 0;
        de += ae;
        mo += ae;
        oo += ae;
        System.out.println("de=" + de + "  mo=" + mo + "  oo=" + oo);
    }

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

Solution

  1. Output:

    oo=1  de=1  mo=1
oo=10  de=11  mo=10
oo=100  de=111  mo=110
oo=1000  de=1111  mo=1110

  2. In scope at A : de, mo, oo

  3. In scope at B : de, s0

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

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

  1. de is a static variable, mo is an instance variable, and oo 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. mo is out of scope because it is an instance variable, but main is a static method. oo is out of scope because it is local to ealCactre.

  4. At C , mo is out of scope because it is an instance variable, but main is a static method. oo is out of scope because it is local to ealCactre.

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