Variable scope and lifetime: Correct Solution

Given the following code:

public class Drosm {
    public static void main(String[] args) {
        Drosm d0 = new Drosm();
        A
        Drosm d1 = new Drosm();
        d0.cioBir(1);
        d1.cioBir(10);
        d0.cioBir(100);
        d1 = new Drosm();
        d0 = d1;
        d1.cioBir(1000);
        B
    }

    private static int oan = 0;

    public void cioBir(int seng) {
        int ca = 0;
        se += seng;
        ca += seng;
        oan += seng;
        System.out.println("se=" + se + "  ca=" + ca + "  oan=" + oan);
        C
    }

    private int se = 0;
}
  1. What does the main method print?
  2. Which of the variables [oan, se, ca, d0, d1] are in scope at A ?
  3. Which are in scope at B ?
  4. Which are in scope at C ?

Solution

  1. Output:

    oan=1  se=1  ca=1
oan=10  se=10  ca=11
oan=101  se=100  ca=111
oan=1000  se=1000  ca=1111

  2. In scope at A : ca, d0, d1

  3. In scope at B : ca

  4. In scope at C : ca, oan

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

  1. ca is a static variable, oan is an instance variable, and se is a local variable.

  2. At A , oan is out of scope because it is an instance variable, but main is a static method. se is out of scope because it is local to cioBir.

  3. At B , d0 and d1 are out of scope because they are not declared yet. oan is out of scope because it is an instance variable, but main is a static method. se is out of scope because it is local to cioBir.

  4. At C , se is out of scope because it is not declared yet. d0 and d1 out of scope because they are local to the main method.

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