How many String objects will be created?

[Syed Salman Ahmad]

public String makinStrings() {
String s = "Fred";
s = s + "47";
s = s.substring(2, 5);
s = s.toUpperCase();
return s.toString();
}
How many String objects will be created when this method is invoked?

[Mahesh Kamath]

Five is the answer.

1. "Fred";
2. "47";
3. Outcome of s + "47"
4. Outcome of s.substring(2, 5);
5. Outcome of s.toUpperCase();

[Amrit Kashyap]

I think it's 6.

The last return call is also creating a String object which is being returned.

[Manfred Klug]

Three is the answer.

1. Outcome of s + "47"
2. Outcome of s.substring(2, 5);
3. Outcome of s.toUpperCase();

For an explanation, you should read the following article:

Strings, Literally

[Manfred Klug]

Originally posted by Devashish Roy:
I think it's 6.

The last return call is also creating a String object which is being returned.

API documentation of String.toString:

This object (which is already a string!) is itself returned.

[Vikash Agarwal]

Fred,
does that mean that "if i have two reference variable pointing to a single String object, and we have a concatenation (or any string manipulation) performed on the object using one reference, then the second reference would still point to the original unmanipulated String?"

[Syed Salman Ahmad]

Manfred, don't you think "Fred" and "47" are not objects. I think they are!.
Because every string literal is a string object which belong to string pool.
That's why i think answer is 5 .

[Amrit Kashyap]

hi fred,


Ok in that case answer is still 5 and not 3. Technically, behind the scene, jvm also creates two String objects for "Fred" and "47".

[Manfred Klug]

Originally posted by Vikash Agarwal:
does that mean that "if i have two reference variable pointing to a single String object, and we have a concatenation (or any string manipulation) performed on the object using one reference, then the second reference would still point to the original unmanipulated String?"

Yes.

public class Test {
public static void main(String... args) {
String s1 = "String";
String s2 = s1;

s1 = s1.concat(" 47");

System.out.println(s1);
System.out.println(s2);
}
}

The output is:
String 47
String

[Manfred Klug]

Originally posted by Syed Salman Ahmad:
Manfred, don't you think "Fred" and "47" are not objects. I think they are!.
Because every string literal is a string object which belong to string pool.
That's why i think answer is 5 .

"Fred" and "47" are objects. But the question is:

How many String objects will be created when this method is invoked?

[Mallik Avula]

i think Devashish Roy is right
"fred" and "47" also string objects only
as Manfred Klug said
toString() method will return same object only, no more creation of object
so total will be 5 objects

regards
Mallik Avula

[Manfred Klug]

Hi Mallik,

you should really read the article I mentioned above.









There are questions you should never answer.

[Raghavan Muthu]

Thats correct Manfred.

Hi syed,

Though the String literals are also String Objects in Heap which points to the Literals in the Literal Pool, but being the String Literals they are picked up when the during the class-loading operation.

Thats why the answer was 3 instead of 5.

quote:How many String objects will be created when this method is invoked?

That was a good point of observation ManFred!

[Raghavan Muthu]

Yes, toString() does NOT return a New String if this method is invoked on a String. But this does return a new string when invoked on other non-String objects.

Carey McGlone's "Strings, Literally" - article is one of the excellent articles. Guys, please go through it and i bet its worth spending your time!!
[ June 19, 2007: Message edited by: Raghavan Muthu ]

[Syed Salman Ahmad]

Thanks Everybody especially Raghavan for explaining it.

[Mahesh Kamath]

Thanks a lot Manfred.

[Raghavan Muthu]

Of course, ManFred is the * Man NOT to be missed here *!!

Thanks Manfred for the active replies