confuse about StringBuffer insert method

[dx wu]

I think the fellowing code result ababcdcd,and why it is abababcd?

public class StringBufferTest{
public static void main(String[] args){
StringBuffer sb = new StringBuffer("abcd");

System.out.println(sb.insert(2,sb));
}
}

[agrah upadhyay]

hello,
Signature of insert Method Is As Follows
1).public synchronized StringBuffer insert(int offset,
Object obj)
2).public synchronized StringBuffer insert(int offset,
String str)
3).public synchronized StringBuffer insert(int offset,
char str[])
4).public StringBuffer insert(int offset,
boolean b)
5).public synchronized StringBuffer insert(int offset,
char c)
6).public StringBuffer insert(int offset, //overloaded for long,
int i) //float,double...too

################################################333
Agrah Upadhyay
3rd Year
B.Tech

[Sandeep Chhabra]

Hello Aghra,
i dont think just telling someone the signatures of a method would help him solve his problem, or help him learning.
if you know why he has got the above mentioned result. then you are requested to please expalin the procedure.
it would be great help for everyone.

Thanx

Sandy

[Ganesh Prakhya]

Hi Dx Wu,

I executed your programme I got the following output. I think this is what you expected.

"ababcdcd"

Regards,
Ganesh..

[Sandeep Chhabra]

Hi Ganesh,
But i am getting the same result as of dx wu

abababcd

Please Explain

Sandy

[Dao Kia]

Hi everyone, i am newbie to this forum.

I just tried with sb.insert(1,sb)

The result is "aaaaabcd"

[Jimmy Thomas]

This is the output that I got: abababcd
Tested on Win2k - Java 5 version.

First of all we must remember that the StringBuffer ultimately uses a Char array to store the contents of the string. Since we're using the same buffer object to do the insert, we're modifying the contents of the underlying array inturn. This is what is actually happening...

StringBuffer sb = new StringBuffer("abcd");

The above line creates a Char array containing {'a','b','c','d'}

sb.insert(2,sb);

Now are trying to insert at index two of the above created array, the point to note is that both the source & destination is the same char array. Initially the array len=4, during copy this what happens..

element 1 --> {'a','b','a','c','d'}
element 2 --> {'a','b','a','b','c','d'}
element 3 --> {'a','b','a','b','a','c','d'}
element 4 --> {'a','b','a','b','a','b','c','d'}
[ September 16, 2005: Message edited by: Jimmy Thomas ]

[sangeetha balasubramaniam]

Hi,

I got the result as ababcdcd what you expected.
I am really confused as why everyone is getting a different answer, can some help us please



Thanks in Advance,
Sangeetha

[sangeetha balasubramaniam]

Hi Jimmy,
Can you explain the element 3 and element 4. i have a doubt as why it agian inserts the char a in element 3 and char b in element 4.

[Jimmy Thomas]

Sangeeta,

I tried the same program on Linux (JDK 1.4.2) $ I got the same that you've pointed out ababcdcd . I suspect there's some change in Implementation between the two version of JDK or due to the platform difference.

Could you tell me on what platform/JDK did you test ???

Can you explain the element 3 and element 4. i have a doubt as why it agian inserts the char a in element 3 and char b in element 4.

The key is the array we're reading from & inserting to are the same. So the 3rd element will the element that's inserted in the first loop & similarly for the 4th element.

[sangeetha balasubramaniam]

Hi Jimmy,
i am using windows xp / jdk 1.3.1_15

[Jimmy Thomas]

There change in implementation between the JDKs (1.5 & 1.4), in JDK 5 the insert method call gets delegated to the insert() of AbstractStringBuilder class. This is not a public class & I couldn't find the docs for the same.

Prior to JDK 5 the insert method functionality was handled by the StringBuffer class itself.

I guess this is the cause for the different outputs that we're getting...
[ September 16, 2005: Message edited by: Jimmy Thomas ]

[sangeetha balasubramaniam]

Hi Jimmy,
i am using windows xp / jdk 1.3.1_15

[Arvind Giri]

Hi Friends,
i think if all of you will mention the jdk version, then it will be more clear.