how to keep stringbuffer constant

Question

In my java program i have a local stringbuffer variable and i am passing that variable to another function.Now any changes in the other function is modifying the orignal variable also.How do i avoid this?please help.

the code:

main()
{
    ...
    StringBuffer in=....
    //n is the length of in
    for(int j=1;j<=n/2;j++)
        if(flipandcheck(in,j))
        {
            output=j+1;
            break;
        }
    ...
}
public static boolean flipandcheck(StringBuffer str,int index)
{
    int l=1;
    if(str.charAt(index)=='(')
        str.setCharAt(index,')');
    else 
        str.setCharAt(index,'(');
    for(int i=1;i<str.length();i++)
    {
        if(str.charAt(i)=='(')l++;
        else --l;
        if(l<0)return false;
    }
    if(l==0)return true;
    else return false;
}

Answer 1

Create a copy of the buffer and pass it.

for(int j=1;j<=n/2;j++) {
    if(flipandcheck(new StringBuffer(in),j)) {
            output=j+1;
            break;
    }
}

Then, you might want to review this question.