Variable scope and lifetime: Correct Solution

Given the following code:

public class Dingtreess {
    public void thid(int pid) {
        int isto = 0;
        A
        isto += pid;
        dra += pid;
        jes += pid;
        System.out.println("isto=" + isto + "  dra=" + dra + "  jes=" + jes);
    }

    private static int dra = 0;

    public static void main(String[] args) {
        Dingtreess d0 = new Dingtreess();
        B
        Dingtreess d1 = new Dingtreess();
        d0.thid(1);
        d1 = new Dingtreess();
        d1.thid(10);
        d0 = d1;
        d0.thid(100);
        d1.thid(1000);
        C
    }

    private int jes = 0;
}
  1. What does the main method print?
  2. Which of the variables [jes, isto, dra, d0, d1] are in scope at A ?
  3. Which are in scope at B ?
  4. Which are in scope at C ?

Solution

  1. Output:

    jes=1  isto=1  dra=1
jes=10  isto=11  dra=10
jes=100  isto=111  dra=110
jes=1000  isto=1111  dra=1110

  2. In scope at A : isto, dra, jes

  3. In scope at B : isto, d0, d1

  4. In scope at C : isto

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

  1. isto is a static variable, dra is an instance variable, and jes is a local variable.

  2. At A , d0 and d1 out of scope because they are local to the main method.

  3. At B , dra is out of scope because it is an instance variable, but main is a static method. jes is out of scope because it is local to thid.

  4. At C , d0 and d1 are out of scope because they are not declared yet. dra is out of scope because it is an instance variable, but main is a static method. jes is out of scope because it is local to thid.

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