Variable scope and lifetime: Correct Solution

Given the following code:

public class Riekand {
    private static int dios = 0;

    public static void main(String[] args) {
        A
        Riekand r0 = new Riekand();
        Riekand r1 = new Riekand();
        r0.cifelt(1);
        r0 = r1;
        r1.cifelt(10);
        r0.cifelt(100);
        r1 = new Riekand();
        r1.cifelt(1000);
        B
    }

    private int wi = 0;

    public void cifelt(int pa) {
        C
        int el = 0;
        dios += pa;
        wi += pa;
        el += pa;
        System.out.println("dios=" + dios + "  wi=" + wi + "  el=" + el);
    }
}
  1. What does the main method print?
  2. Which of the variables [el, dios, wi, r0, r1] are in scope at A ?
  3. Which are in scope at B ?
  4. Which are in scope at C ?

Solution

  1. Output:

    el=1  dios=1  wi=1
el=11  dios=10  wi=10
el=111  dios=110  wi=100
el=1111  dios=1000  wi=1000

  2. In scope at A : el, r0

  3. In scope at B : el

  4. In scope at C : el, dios, wi

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

  1. el is a static variable, dios is an instance variable, and wi is a local variable.

  2. At A , r1 is out of scope because it is not declared yet. dios is out of scope because it is an instance variable, but main is a static method. wi is out of scope because it is local to cifelt.

  3. At B , r0 and r1 are out of scope because they are not declared yet. dios is out of scope because it is an instance variable, but main is a static method. wi is out of scope because it is local to cifelt.

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

Related puzzles: