Question

this question is like my previous one
Given:

3. interface Animal { void makeNoise(); }
4. class Horse implements Animal {
5.   Long weight = 1200L;
6.   public void makeNoise() { System.out.println("whinny"); }
7.  }
8.  public class Icelandic extends Horse {
9.   public void makeNoise() { System.out.println("vinny"); }
10.  public static void main(String[] args) {
11.    Icelandic i1 = new Icelandic();
12.    Icelandic i2 = new Icelandic();
13.    Icelandic i3 = new Icelandic();
14.    i3 = i1; i1 = i2; i2 = null; i3 = i1;
15.  }
16. }

When line 14 is reached, how many objects are eligible for the garbage collector?

A. 0

B. 1

C. 2

D. 3

E. 4

F. 6

I chose A but the right answer is E, but I don’t know Why?

Answer 1

Let’s call the three Icelandic objects created in main as A, B and C.

Initialy

• i1=A, i2=B and i3=C;

After i3 = i1

• i1=A, i2=B and i3=A;

After i1 = i2

• i1=B, i2=B and i3=A;

After i2 = null:

• i1=B, i2=null and i3=A;

After i3 = i1

• i1=B, i2=null and i3=B

In line 14, there are standing references to only B object of type Icelandic. A and C are lost in the running program.

Each Icelandic object that is lost gives garbage collector two objects to collect, ie. the Icelandic object itself and the Long object within every Icelandic, which make the total number of garbage collected objects 4.

Since makeNoise methods are never called, they do not change the outcome.