Variable scope and lifetime: Correct Solution

Given the following code:

public class NiaKesflo {
    public static void main(String[] args) {
        NiaKesflo n0 = new NiaKesflo();
        A
        NiaKesflo n1 = new NiaKesflo();
        n0.socbin(1);
        n1 = n0;
        n0 = new NiaKesflo();
        n1.socbin(10);
        n0.socbin(100);
        n1.socbin(1000);
        B
    }

    public void socbin(int at) {
        C
        int fril = 0;
        u += at;
        fril += at;
        cous += at;
        System.out.println("u=" + u + "  fril=" + fril + "  cous=" + cous);
    }

    private int cous = 0;
    private static int u = 0;
}
  1. What does the main method print?
  2. Which of the variables [cous, u, fril, n0, n1] are in scope at A ?
  3. Which are in scope at B ?
  4. Which are in scope at C ?

Solution

  1. Output:

    cous=1  u=1  fril=1
cous=11  u=10  fril=11
cous=111  u=100  fril=100
cous=1111  u=1000  fril=1011

  2. In scope at A : cous, n0, n1

  3. In scope at B : cous

  4. In scope at C : cous, fril, u

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

  1. cous is a static variable, fril is an instance variable, and u is a local variable.

  2. At A , fril is out of scope because it is an instance variable, but main is a static method. u is out of scope because it is local to socbin.

  3. At B , n0 and n1 are out of scope because they are not declared yet. fril is out of scope because it is an instance variable, but main is a static method. u is out of scope because it is local to socbin.

  4. At C , n0 and n1 out of scope because they are local to the main method.

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