Variable scope and lifetime: Correct Solution

Given the following code:

public class Einel {
    private static int u = 0;

    public void zess(int he) {
        int ec = 0;
        A
        u += he;
        aved += he;
        ec += he;
        System.out.println("u=" + u + "  aved=" + aved + "  ec=" + ec);
    }

    public static void main(String[] args) {
        Einel e0 = new Einel();
        B
        Einel e1 = new Einel();
        e0.zess(1);
        e0 = new Einel();
        e1 = e0;
        e1.zess(10);
        e0.zess(100);
        e1.zess(1000);
        C
    }

    private int aved = 0;
}
  1. What does the main method print?
  2. Which of the variables [ec, u, aved, e0, e1] are in scope at A ?
  3. Which are in scope at B ?
  4. Which are in scope at C ?

Solution

  1. Output:

    ec=1  u=1  aved=1
ec=11  u=10  aved=10
ec=111  u=110  aved=100
ec=1111  u=1110  aved=1000

  2. In scope at A : ec, u, aved

  3. In scope at B : ec, e0, e1

  4. In scope at C : ec

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

  1. ec is a static variable, u is an instance variable, and aved is a local variable.

  2. At A , e0 and e1 out of scope because they are local to the main method.

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

  4. At C , e0 and e1 are out of scope because they are not declared yet. u is out of scope because it is an instance variable, but main is a static method. aved is out of scope because it is local to zess.

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