To determine when a single object becomes eligible for garbage collection (GC), we need to understand the concept of object references and the conditions for GC.
In this program, the class Eco
has a reference variable e
of type Eco
. The main
method creates three instances of the Eco
class: e1
, e2
, and e3
.
Let's go through each line of the code and analyze the changes:
Eco e;
- Declares a reference variable e
without initializing it.
Eco e1 = new Eco();
- Creates a new object of the Eco
class and assigns its reference to e1
.
Eco e2 = new Eco();
- Creates a new object of the Eco
class and assigns its reference to e2
.
Eco e3 = new Eco();
- Creates a new object of the Eco
class and assigns its reference to e3
.
e3.e = e2;
- Assigns the reference of e2
to the instance variable e
of the e3
object. This creates a circular reference between e2
and e3
.
e1.e = e3;
- Assigns the reference of e3
to the instance variable e
of the e1
object.
e2 = null;
- Sets the e2
reference variable to null
. This means that the object originally referenced by e2
is no longer accessible.
e3 = null;
- Sets the e3
reference variable to null
. This means that the object originally referenced by e3
is no longer accessible.
e2.e = el;
- Throws a NullPointerException
. Since e2
is null
, trying to access e2.e
results in an exception.
e1 = null;
- Sets the e1
reference variable to null
. This means that the object originally referenced by e1
is no longer accessible.
Based on the code execution, let's analyze when each object becomes eligible for GC:
e1
becomes eligible for GC after line 11 runs because the reference to the object is set to null
.
e2
becomes eligible for GC after line 8 runs because the reference to the object is set to null
.
e3
becomes eligible for GC after line 9 runs because the reference to the object is set to null
.
- The object referenced by
e2
becomes eligible for GC after line 10 runs because it is no longer accessible.
Therefore, at the end of the program, there is no object left that is eligible for GC. Hence, the correct answer is F. Never in this program.
The given correct answer, E. An exception is thrown at runtime, is incorrect because the exception is thrown before any object becomes eligible for GC.