Trouble with string modifications

Question

i need to modify the string parameter "line" to insert a space before and after all punctuation such as ". , ' " " - ) ( ; ".
so the line System.out.print should output as System . out . print
and " I am your father. - Darth vader" into "I am your father . - Darth vader
this is what I have so far but it does not work(btw punc. is defined as string " . , ' \" ( ) ; -"
for(int i=0;(line.length()-1)>i;i++)// go through all letters to find punc.
              char n = line.charAt(i);
              System.out.print(n);
              if((punc.indexOf(n))>-1)//if char is a punc. add space before and after it
                   String begin=line.substring(0,i);
                   String middle=line.substring(i,i+1);
                   String end=line.substring(i+1);
                   line = begin+" "+middle+" "+end;
              }//end if
          }//end for

Answer 1

when i print out " i " it just gives a infinite loop
of index values.Think about it.
Suppose it finds a punctuation mark at position 15.
It then replaces line with a new version of line, with a space at position 15, the same punctuation mark at position 16, and another space at position 17.
Then i is incremented.
What will it find on position 16?
What do you mean by pass line to the caller?Does your method end with this:
return line;If not, how does the changed version of line get to the code that called the method you're writing?