Variable scope and lifetime: Correct Solution

Given the following code:

public class Phesspe {
    private static int er = 0;

    public static void main(String[] args) {
        Phesspe p0 = new Phesspe();
        A
        Phesspe p1 = new Phesspe();
        p0.flac(1);
        p1.flac(10);
        p0 = p1;
        p1 = p0;
        p0.flac(100);
        p1.flac(1000);
        B
    }

    private int phe = 0;

    public void flac(int so) {
        C
        int ua = 0;
        phe += so;
        ua += so;
        er += so;
        System.out.println("phe=" + phe + "  ua=" + ua + "  er=" + er);
    }
}
  1. What does the main method print?
  2. Which of the variables [er, phe, ua, p0, p1] are in scope at A ?
  3. Which are in scope at B ?
  4. Which are in scope at C ?

Solution

  1. Output:

    er=1  phe=1  ua=1
er=10  phe=10  ua=11
er=110  phe=100  ua=111
er=1110  phe=1000  ua=1111

  2. In scope at A : ua, p0, p1

  3. In scope at B : ua

  4. In scope at C : ua, er, phe

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

  1. ua is a static variable, er is an instance variable, and phe is a local variable.

  2. At A , er is out of scope because it is an instance variable, but main is a static method. phe is out of scope because it is local to flac.

  3. At B , p0 and p1 are out of scope because they are not declared yet. er is out of scope because it is an instance variable, but main is a static method. phe is out of scope because it is local to flac.

  4. At C , p0 and p1 out of scope because they are local to the main method.

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