Variable scope and lifetime: Correct Solution

Given the following code:

public class Trec {
    private int ir = 0;

    public static void main(String[] args) {
        Trec t0 = new Trec();
        A
        Trec t1 = new Trec();
        t0.merhop(1);
        t0 = t1;
        t1.merhop(10);
        t1 = t0;
        t0.merhop(100);
        t1.merhop(1000);
        B
    }

    public void merhop(int na) {
        C
        int fing = 0;
        ir += na;
        fing += na;
        be += na;
        System.out.println("ir=" + ir + "  fing=" + fing + "  be=" + be);
    }

    private static int be = 0;
}
  1. What does the main method print?
  2. Which of the variables [be, ir, fing, t0, t1] are in scope at A ?
  3. Which are in scope at B ?
  4. Which are in scope at C ?

Solution

  1. Output:

    be=1  ir=1  fing=1
be=10  ir=10  fing=11
be=110  ir=100  fing=111
be=1110  ir=1000  fing=1111

  2. In scope at A : fing, t0, t1

  3. In scope at B : fing

  4. In scope at C : fing, be, ir

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

  1. fing is a static variable, be is an instance variable, and ir is a local variable.

  2. At A , be is out of scope because it is an instance variable, but main is a static method. ir is out of scope because it is local to merhop.

  3. At B , t0 and t1 are out of scope because they are not declared yet. be is out of scope because it is an instance variable, but main is a static method. ir is out of scope because it is local to merhop.

  4. At C , t0 and t1 out of scope because they are local to the main method.

Related puzzles: