Appending a character to a string

Question

Hi I am trying to read in a sequence of numbers from a file, theyre of the form: 0.034 0.113 0.987 etc. What i am trying to do is read in the line of these numbers, and if we are not at a space in the numbers or at the end of file I want to append the numbers to a stringbuffer called TempHelix. For some reason my program keeps getting an error inside my while loop. Any help is appreciated
StringBuffer TempHelix = null;
int index = 0;
if((current.charAt(index) != ' ') && index <current.length()){
//PROBLEM HERE
TempHelix = TempHelix.append(current.charAt(index));
//NOW WE GET THE STRING THAT HAS BEEN MADE UP IN THE
//LOOP AND PARSE TO A DOUBLE AND THEN INSERT INTO AN ARRAY
String s = new String(TempHelix);
TempDouble = Double.parseDouble(s);
Helix[index] = TempDouble;
index++
//after adding to index we go back into loop and continue
}

Answer 1

here is what i have modified so far:
           double TempDouble = 0;
             int index = 0;
             if((current=dis.readLine()) != null){          
             StringBuffer TempHelix = new StringBuffer(null);
                          if((current.charAt(index)!= ' ')){
                                   //PROBLEM HERE
                                   TempHelix.append(current.charAt(index));
                                   //TempHelix = TempHelix + current.charAt(index);
                                   String s = TempHelix.toString();
                              TempDouble = Double.parseDouble(s);
                                   Helix[index] = TempDouble;
                              System.out.println(Helix[index]);
                              index++;
     }