Variable scope and lifetime: Correct Solution

Given the following code:

public class Aenti {
    public static void main(String[] args) {
        A
        Aenti a0 = new Aenti();
        Aenti a1 = new Aenti();
        a0.mosm(1);
        a1.mosm(10);
        a0 = new Aenti();
        a0.mosm(100);
        a1 = new Aenti();
        a1.mosm(1000);
        B
    }

    public void mosm(int mo) {
        C
        int ded = 0;
        wi += mo;
        fo += mo;
        ded += mo;
        System.out.println("wi=" + wi + "  fo=" + fo + "  ded=" + ded);
    }

    private static int fo = 0;
    private int wi = 0;
}
  1. What does the main method print?
  2. Which of the variables [ded, wi, fo, a0, a1] are in scope at A ?
  3. Which are in scope at B ?
  4. Which are in scope at C ?

Solution

  1. Output:

    ded=1  wi=1  fo=1
ded=10  wi=11  fo=10
ded=100  wi=111  fo=100
ded=1000  wi=1111  fo=1000

  2. In scope at A : wi, a0

  3. In scope at B : wi

  4. In scope at C : wi, ded, fo

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

  1. wi is a static variable, ded is an instance variable, and fo is a local variable.

  2. At A , a1 is out of scope because it is not declared yet. ded is out of scope because it is an instance variable, but main is a static method. fo is out of scope because it is local to mosm.

  3. At B , a0 and a1 are out of scope because they are not declared yet. ded is out of scope because it is an instance variable, but main is a static method. fo is out of scope because it is local to mosm.

  4. At C , a0 and a1 out of scope because they are local to the main method.

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