It's working perfectly and I'm using FileWriter but it still complains..

Thanks mate. Tried that already, doesn't work..

The commas wouldn't be placed correctly. Consider a line such as: sixteen seven twenties log The output would be: sixteen,twenties, where the last comma would be added because "log" follows "twenties" even though it won't be added. If the file was more than one line: sixteen seven twenties sixteen seven twenties sixteen seven twenties The output would be sixteen,twentiessixteen,twentiessixteen,twenties Where there is no comma twentiessixteen (which occurs because a new line is taken). One thing that you should try not to do is have more than one stream open at any one time in code. Also, each individual read/write takes time, so making sure to only do one read or one write will be quite a bit more efficient. If you have to make multiple read/writes, then a Buffered Reader/Writer is more efficient than a non-buffered one. So.... In this task you should remove the writing from the loop that reads, and instead (using the same technique) just add all the appropriate words to a list. Then after the Reader is closed, open a Writer and write all the words. This time, since you pre-processed all the words in the list, adding a comma as long as there are more words is appropriate. Here are some other techniques I use to append chars like commas or spaces into things like this:

write(list.get(0)); // write the first word in the list
// then start at index 1 because you don't need to write 0 again
for(int i = 1; i < list.size(); i++){
   // and write all the rest of the words starting with the separator
   write("," + list.get(i));
}

or with an iterator:

Iterator it = list.iterator();
while(true) { // infinite loop
   write(it.next());
   if(!it.hasNext()) break; // no more values, break loop
   write(","); // writes comma
}

The comma wont be reached if there are no more values

I have a file that has ~160,000 characters in it, something I copied and pasted from wikipedia. I timed how fast reading the full file was by using: BufferedReader.read() // reads each individual byte BufferedReader.readLine() // reads a full line FileReader.read() //reads each individual char FileReader.read(char[]) // read all the chars into this array in one shot FileInputStream.read() //reads each individual byte FileIntputStream.read(byte[]) // read all bytes into this array in one shot Here are the results in milliseconds (1000 equals 1 second): BufferedReader.read() in ms: 23 BufferedReader.readLine() in ms: 11 FileReader.read() in ms: 48 FileReader.read(char[] ALLCHARS) in ms: 0 FileInputStream.read() in ms: 1640 FileInputStream.read(byte[] ALLBYTES) in ms: 0

Hmm, bad news. Arrays should be used. But I like readLine() and I have some time. So, let it be 11 ms ;) Thanks for the data.

Thanks a lot mate. Brilliant infos as always. I'm gonna leave this open as I'm sure it will be helpful to many others...

Lupe, You wrote: "One thing that you should try not to do is have more than one stream open at any one time in code." But why is it a problem if several streams are open at the same time? (They've shown us examples of this several times in lessons, for example in file copying example codes. A set of data is read from one stream and we immediately put it into another.) And if the file size is extremely huge, isn't it a problem if I copy the whole file content into an array (into the memory)? Instead of directly into a Writer.

Streams are very resource intensive, one of the slowest parts of the program. Of course, when you have files that are gigabytes large then saving them in memory is not going to be an effective solution, however for the purpose of tasks I have not run into any problems with reading everything into memory and then writing the source. Me, personally, I like to find the fastest algorithm possible.