Variable scope and lifetime: Correct Solution

Given the following code:

public class Romu {
    private static int wuo = 0;
    private int ilu = 0;

    public void earm(int u) {
        A
        int a = 0;
        wuo += u;
        a += u;
        ilu += u;
        System.out.println("wuo=" + wuo + "  a=" + a + "  ilu=" + ilu);
    }

    public static void main(String[] args) {
        Romu r0 = new Romu();
        B
        Romu r1 = new Romu();
        C
        r0.earm(1);
        r1 = r0;
        r1.earm(10);
        r0.earm(100);
        r0 = new Romu();
        r1.earm(1000);
    }
}
  1. What does the main method print?
  2. Which of the variables [ilu, wuo, a, r0, r1] are in scope at A ?
  3. Which are in scope at B ?
  4. Which are in scope at C ?

Solution

  1. Output:

    ilu=1  wuo=1  a=1
ilu=11  wuo=10  a=11
ilu=111  wuo=100  a=111
ilu=1111  wuo=1000  a=1111

  2. In scope at A : ilu, a, wuo

  3. In scope at B : ilu, r0, r1

  4. In scope at C : ilu, r0, r1

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

  1. ilu is a static variable, a is an instance variable, and wuo is a local variable.

  2. At A , r0 and r1 out of scope because they are local to the main method.

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

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

Related puzzles: