Variable scope and lifetime: Correct Solution

Given the following code:

public class Cijun {
    public void axoPrea(int fe) {
        int oco = 0;
        A
        oco += fe;
        ho += fe;
        of += fe;
        System.out.println("oco=" + oco + "  ho=" + ho + "  of=" + of);
    }

    private static int of = 0;
    private int ho = 0;

    public static void main(String[] args) {
        Cijun c0 = new Cijun();
        B
        Cijun c1 = new Cijun();
        c0.axoPrea(1);
        c0 = c1;
        c1.axoPrea(10);
        c0.axoPrea(100);
        c1 = new Cijun();
        c1.axoPrea(1000);
        C
    }
}
  1. What does the main method print?
  2. Which of the variables [of, oco, ho, c0, c1] are in scope at A ?
  3. Which are in scope at B ?
  4. Which are in scope at C ?

Solution

  1. Output:

    of=1  oco=1  ho=1
of=10  oco=10  ho=11
of=100  oco=110  ho=111
of=1000  oco=1000  ho=1111

  2. In scope at A : ho, oco, of

  3. In scope at B : ho, c0, c1

  4. In scope at C : ho

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

  1. ho is a static variable, oco is an instance variable, and of is a local variable.

  2. At A , c0 and c1 out of scope because they are local to the main method.

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

  4. At C , c0 and c1 are out of scope because they are not declared yet. oco is out of scope because it is an instance variable, but main is a static method. of is out of scope because it is local to axoPrea.

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