Variable scope and lifetime: Correct Solution

Given the following code:

public class Uirds {
    public void pnec(int mo) {
        int mafe = 0;
        A
        crun += mo;
        neas += mo;
        mafe += mo;
        System.out.println("crun=" + crun + "  neas=" + neas + "  mafe=" + mafe);
    }

    private static int neas = 0;
    private int crun = 0;

    public static void main(String[] args) {
        Uirds u0 = new Uirds();
        B
        Uirds u1 = new Uirds();
        u0.pnec(1);
        u1.pnec(10);
        u0.pnec(100);
        u0 = u1;
        u1 = u0;
        u1.pnec(1000);
        C
    }
}
  1. What does the main method print?
  2. Which of the variables [mafe, crun, neas, u0, u1] are in scope at A ?
  3. Which are in scope at B ?
  4. Which are in scope at C ?

Solution

  1. Output:

    mafe=1  crun=1  neas=1
mafe=10  crun=11  neas=10
mafe=101  crun=111  neas=100
mafe=1010  crun=1111  neas=1000

  2. In scope at A : crun, mafe, neas

  3. In scope at B : crun, u0, u1

  4. In scope at C : crun

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

  1. crun is a static variable, mafe is an instance variable, and neas is a local variable.

  2. At A , u0 and u1 out of scope because they are local to the main method.

  3. At B , mafe is out of scope because it is an instance variable, but main is a static method. neas is out of scope because it is local to pnec.

  4. At C , u0 and u1 are out of scope because they are not declared yet. mafe is out of scope because it is an instance variable, but main is a static method. neas is out of scope because it is local to pnec.

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