StringBuffer and String Confused!!

[asha ganapathy]

I wrote this piece of code

line 1:  StringBuilder sb = new StringBuilder("Foo");
line 2:  sb.append("bar").delete(2, 4).reverse().insert(2, "tt"); //rattoF
line 3:  String s7 = sb.toString().substring(1, 5);rattbFoar
line 4:  s7.toUpperCase();
line 5:  System.out.println(s7);

Till line no.2 i understood the output, but line no.3 output i didnt understand how the output is rattbFoar.
pls someone explain me

[dolly shah]

Hi Asha,

public class Feline {
    public static void main(String... args){
        StringBuilder sb = new StringBuilder("Foo");
  sb.append("bar").delete(2, 4).reverse().insert(2, "tt"); //rattoF
  String s7 = sb.toString().substring(1, 5);//rattbFoar
  s7.toUpperCase();
  System.out.println(s7);
    }
}

From where you found output. I wrote code I got output "atto". That was I also answered.


It looks like you are taking "Java.Inquisition" mock exam. I am also taking that only. I have just posted my doubt about "Drag & Drop" question. If you know can you please help me. I am little stuck over there. I appreciate your help.

[asha ganapathy]

Hi Dolly,

I got the output by executing on my machine..yes even i am using the same mock exam.Even i thought the output should have been "atto".
But after executing this code i found that
String s7 = sb.toString().substring(1, 5);
gives magically this output "rattbFoar", i wanted to know how toString() function performs.

Asha

[asha ganapathy]

Yes Dolly if i know the answer to your question i can surely help you out

[Jesper de Jong]

Originally posted by asha ganapathy:
Hi Dolly,

I got the output by executing on my machine..yes even i am using the same mock exam.Even i thought the output should have been "atto".
But after executing this code i found that
String s7 = sb.toString().substring(1, 5);
gives magically this output "rattbFoar", i wanted to know how toString() function performs.

Asha

Hello Asha, are you really sure that you got "rattbFoar"? Because I tried running it and got "atto". If you look at the call: substring(1, 5) will give you a string of 4 characters. So the output can never be "rattbFoar".

So check your code - probably your test program is not exactly the same as the code above, or you have an old version of a class file somewhere, etc.

[dolly shah]

i wanted to know how toString() function performs.

toString()converts StringBuilder or StringBuffer in String.

[asha ganapathy]

oh i guess it was running with an older version of .class file
Thanks a lot

[Nicholas Jordan]

Originally posted by asha ganapathy:
oh i guess it was running with an older version of .class file

I doubt that would cause a failure as described.

public class StringConfused{
    public static void main(String[]args)
    {
        // prints out atto
        StringBuilder sb = new StringBuilder("Foo");
        sb.append("bar").delete(2, 4).reverse().insert(2, "tt"); //rattoF
        String s7 = sb.toString().substring(1, 5);//rattbFoar
        s7.toUpperCase();System.out.println(s7);
    }
}

javac 1.5.0_12

java version "1.5.0_12"

In general, toString often constructs a new String reference.

But not always:

[asha ganapathy:] ... wanted to know how toString() function performs.

/*
* @(#)StringBuilder.java 1.9 04/07/16
*
*/
public String toString() {
    // Create a copy, don't share the array
    return new String(value, 0, count);
}
 
 
/**
*
* @(#)String.java   1.189 05/10/21
*
* This object (which is already a string!) is itself returned.
*
* @return  the string itself.
*/
public String toString() {
return this;
}
 

Try not to guess unless you are investigating borderline conditions or doing intentionally exploratory work.



re:

One more clarification required..what is equals() method used for?
s1.equals(s2) -> checks if both Strings have same value or not?
please correct me if i am wrong.

posted Sunday, August 05, 2007 8:07 PM in Java (beginner) Strings
t = 023603 (topic)
f=33 (forum)

In general, == should be used to test for equality of primitives,

use dot equals for everything else .... there is no substitute for testing.

[ August 30, 2007: Message edited by: Nicholas Jordan ]