how many objects are eligible for garbage collection?

[william tham]

From the following code how many objects are eligible for garbage collection?
String string1 = "Test";
String string2 = "Today";
string1 = null;
string1 = string2;
A) 1
B) 2
C) 3
D) 0

[Percy Densmore]

"Test" is the only object that is not being referenced after execution. Both are currently pointing to "Today". So my answer would be: A)1
Percy

[Jimmy Blakely]

The answer is 0.
String literals are not garbage collected.
However if the code was written like this....
String string1 = new String("Test");
String string2 = new String("Today");
string1 = null;
string1 = string2;
The answer would be 1.

[Percy Densmore]

Thanks for the clarification, Jimmy. I knew better

------------------
Percy Densmore
-SCJP2 Die Hard Student

[Anonymous]

Percy Densmore you answer is correct. "test" has not be reffernce after the first execution, therefore it is eligible for garbage collection. a. 1 "is the answer"

[Anonymous]

I have to agree with Jimmy.
The J2SE API spec for the String.intern() method states "A pool of strings, initially empty, is maintained privately by the class String." Additionally, "All literal strings and string-valued constant expressions are interned," i.e. they are added to the String pool.
This implies that the String class manages "Test" and "Today" within its private String literal pool. Hence, even if "Test" is no longer referenced, the pool manager may still be holding on to it, thereby preventing the garbage collector from freeing the object from memory.

[kishor rao]

when strings are created with the = operator, they are only stored in the string literal pool. strings in the string literal pool are not eligible for garbage collection

[Dan Chisholm]

I agree with Jimmy: String literals are not garbage collected.
Garbage collection questions involving Strings will not be included on the exam.

[John Lee]

Thanks, Jimmy.

[Dan Chisholm]

This appears to be a question rather than an indication of errata in some unspecified mock exam. I will move it to the Programmer Certification Study forum.

[Jose Botella]

The pool of strings kept by the class String is not the cause that string literals are not g.ced The string objects computed from compile-constant expressions (JLS15.28) may reside on such pool(*); but, they are pointed to by the constant pool of the class declaring the string literals. Thus only downloading (from the JVM) the class where the string literals were declared, it is possible to make them eligible for g.c.
Fortunately this is not a subject for the exam.
(*) I am not saying that literals string objects reside in such a pool. This pool could be just a set of references pointing to the real objects. I do not really know about it. I can only say that objects are in the heap.
[ March 01, 2003: Message edited by: Jose Botella ]