String objects

[Carolyn Nguyen]

Hi all,
I am preparing for SCJP 1.4 and found this question in EXAM CRAM2 Java 2 Programmer (page 59).
How many String objects are created in the following code?
1. String A, B, C;
2. A = new String( "1234" ) ;
3. B = A;
4. C = A + B;
A. One
B. Two
C. Three
D. Four
My guess is C. Three.
Since line 2
A = new String( "1234" ) ;
would create 2 String objects, and line 4
C = A + B;
created another one. But the book's answer is B. Two
Could anyone please explain it. Is there a way that we can check the answer programmatically?
Thanks.
cn

[Sefa Urgenc]

You can try to invoke String methods on those references, and if they are objects they should not give you NullPointerException (I think I should try it, before mentioning it duhh!!).
Sorry that's all I can think of.

[Maulin Vasavada]

hi Carolyn
the only thing i see is- the question asks "String Objects". the two strings that are created in
A = new String("1234");
are essentially,
1. String Object reference A
2. string "literal" "1234"
but out of these String Object is only one.
so in place you counted 2, its only 1 "String Object" which leads to the answer B.
regards
maulin

[Maulin Vasavada]

so..in essence i mean- string literal wasn't considered "String Object"
regards
maulin

[Sefa Urgenc]

Well I did invoke string method length() on those references, and they seem to be working. I do not know how else to classify a if a String reference is an object.

 String A, B, C;
         A = new String("1234");
         B = A;
         C = A + B;
         System.out.println(B.length());
         System.out.println(A.length());
         System.out.println(C.length());  

You get the output of
4
4
8
There is a similar example on the K&B (if you have it) page 359.

[Carolyn Nguyen]

Thanks Sefa and Maulin for respond to my post.
according to sun website
http://java.sun.com/docs/books/tutorial/java/data/stringsAndJavac.html

"compiler automatically creates a new String object for every literal string it encounters, you can use a literal string to initialize a String. " and it goes on to describe that the following line of code
String s = new String("Hola Mundo");
would create two Strings.
"The compiler creates the first string when it encounters the literal string "Hola Mundo!", and the second one when it encounters new String. "

[Anupam Sinha]

Hi Carolyn
The answer is three. But I guess that this type shouldn't be there on the exam because I don't think that asking such questins would make much sense.

[Damien Howard]

K&B's book has a similar example and they count it as three.
The K in K&B is one of the exam co-authors, so if it comes up on the exam, I would go with three.

[Maulin Vasavada]

yeah
this question has always results into long threads of discussion as there seems uncertainty in definition or interpretation and what not ...
to me, i would agree w/ ppl here that this sort of question should not be there in exam but if it is just go w/ what u think. none is gonna take away life from u for ONLY ONE wrong answer out of all if u know what i mean
regards
maulin

[pradeepbill arumalla]

totally at the end of the program we have two different strings so two objects obviously,since the strings which are same are treated as a single object(excluding some special cases),we have 2 string objects.