Variable scope and lifetime: Correct Solution

Given the following code:

public class Fropre {
    private int se = 0;
    private static int o = 0;

    public static void main(String[] args) {
        Fropre f0 = new Fropre();
        A
        Fropre f1 = new Fropre();
        f0.phen(1);
        f1.phen(10);
        f0.phen(100);
        f1 = new Fropre();
        f0 = f1;
        f1.phen(1000);
        B
    }

    public void phen(int glal) {
        int fre = 0;
        fre += glal;
        o += glal;
        se += glal;
        System.out.println("fre=" + fre + "  o=" + o + "  se=" + se);
        C
    }
}
  1. What does the main method print?
  2. Which of the variables [se, fre, o, f0, f1] are in scope at A ?
  3. Which are in scope at B ?
  4. Which are in scope at C ?

Solution

  1. Output:

    se=1  fre=1  o=1
se=10  fre=11  o=10
se=100  fre=111  o=101
se=1000  fre=1111  o=1000

  2. In scope at A : fre, f0, f1

  3. In scope at B : fre

  4. In scope at C : fre, o

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

  1. fre is a static variable, o is an instance variable, and se is a local variable.

  2. At A , o 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 phen.

  3. At B , f0 and f1 are out of scope because they are not declared yet. o 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 phen.

  4. At C , se is out of scope because it is not declared yet. f0 and f1 out of scope because they are local to the main method.

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