How many String Object are created in the following code ??

[Rohan Kayan]

String s1 = "spring ";
String s2 = s1 + "summer ";
s1.concat("fall ");
s2.concat(s1);
s1 += "winter ";
System.out.println(s1 + " " + s2);

[Sandeep Shukla]

String s1 = "spring "; # 1
String s2 = s1 + "summer ";#2
s1.concat("fall "); #3
s2.concat(s1);#4
s1 += "winter ";#5
System.out.println(s1 + " " + s2); #6

//net 6 ....(as + and concatenation operations are stringbuffer operations and the final thing is converted to string)

[Eric Zanders]

Rohan,

I would say 5:
1� s1.
2� s2.
3� The string concatenation is not stored in s1 but it exists.
4� Same case for the s2 string concatenation.
5� The string you'll print is the concatenation s1, a blank and s2.

To verify this I created a little testprogram:

class Test {
public static void main (String args[]) {
String s1 = "spring ";
System.out.println("s1= " + s1); 
String s2 = s1 + "summer ";
System.out.println("s2= " + s2); 
System.out.println("s1.concat= " + s1.concat("fall "));
System.out.println("s1= " + s1); 
System.out.println("s2.concat= " + s2.concat(s1));
System.out.println("s2= " + s2); 
s1 += "winter ";
System.out.println(s1 + " " + s2); 
}
}

When you run this, you'll notice that:
- s1 only gets concatenated with "winter " because of the statement
s1 += "winter "; which is written out in full s1 = s1 + "winter ";
thus resulting in modification of s1.
- s2 is never modified.

Greetz

J

[Paul Sturrock]

thus resulting in modification of s1.

Strings are immutable. You cannot modify a String object.

[Eric Zanders]

Dear Paul,

As I'm only a beginner I tend to make mistakes. (which is normal, I guess...)

Would it have been more correct if I had stated that the content of the object s1 was modified?

Anyway, thanks for correcting me. How else am I going to learn from my mistakes?

Greetz

J

[Paul Sturrock]

Mistakes are expected - we all make them.

Would it have been more correct if I had stated that the content of the object s1 was modified?

No. Think of "immutable" as meaning "read-only". If I write this:

String s1 = "initial string";
s1 = s1 + " more characters";

What I've got is one reference (s1) which points to a String object. In line 1 the reference points the the value "initial string". In line two the value of the object doesn't change (becasue it can't), instead another String object is created with the value of "initial string more characters" and the reference s1 is pointed at that. The original String object still exists, its just no references point to it anymore.

[Eric Zanders]

Thanks Paul.
So returning to the initial question, the result (number of String objects) then should be 6?

[Layne Lund]

I count at least 9:

String s1 = "spring ";             // #1 = "spring ", the reference s1 points directly at it
String s2 = s1 + "summer ";        // #2 = "summer ", #3 = "spring summer " (referenced by s2)
s1.concat("fall ");                // #4 = "fall ", #5 "spring fall " (now referenced by s1)
s2.concat(s1);                     // #5 = "spring summer spring fall " (referenced by s2)
s1 += "winter ";                   // #6 = "winter ", #7 = "spring fall winter " (referenced by s1)
System.out.println(s1 + " " + s2); // #8 = " ", #9 = "spring fall winter  sprint summer spring fall "

Remember that String objects are created for each of the literals in the code.

Layne

[Dirk Schreckmann]

javanic1,

Welcome to JavaRanch!

We ain't got many rules 'round these parts, but we do got one. Please change your display name to comply with The JavaRanch Naming Policy.

Thanks Pardner! Hope to see you 'round the Ranch!

[Rohan Kayan]

String s1 = "spring ";             // #1 = "spring ", the reference s1 points directly at it
String s2 = s1 + "summer ";        // #2 = "summer ", #3 = "spring summer " (referenced by s2)
s1.concat("fall ");                // #4 = "fall ", #5 "spring fall " (now referenced by s1)
s2.concat(s1);                     // #5 = "spring summer spring fall " (referenced by s2)
s1 += "winter ";                   // #6 = "winter ", #7 = "spring fall winter " (referenced by s1)
System.out.println(s1 + " " + s2); // #8 = " ", #9 = "spring fall winter  sprint summer spring fall "

Remember that String objects are created for each of the literals in the code.

Layne[/qb]<hr></blockquote>

You are right that each of the literals in the code will be a string object but from that point of view the count should be 10 as in the last line , when s1 + " " it will create a new string object with s1 and blank in the last. Then again this object will be again concatnated with s2 creating another string object .

[ October 24, 2004: Message edited by: Rohan Kayan ]

[Shailesh Chandra]

I would recommend to read this article about Strings on javaranch itself,
this is very nice article and definitely you will get answer to your question.