Question

I’m trying to process an input file containing numbers that I must use for calculations and characters I need to use for comparisons. A quick example is a file like this:

6
foobar

and code like this:

n = readInInt
  while n > 0
    c = readInSingleChar
    if (c = 'f')
      doSomething
    n--

Currently I’m finding a lot of options on here and via Google, involving DataStream and BufferedReader and FileReader, but there seems like there are too many ways and I’m not sure they all work how I need them too. Please let me know if my need isn’t clear.

In short, I need to read a file character by character, and interpret/use those that are numbers as ints, and those that are letters and symbols as chars.

What’s the simplest way to do this? I know there are professional ways to do things, and “ok” ways to do things. This is for a one-time, hobby-like personal use thing and I’m not looking for solid or robust functionality. It just has to work alright.

Thanks!

Answer 1

I feel the easiest way is to use StreamTokenizer This class gives you the utilities needed to parse ints or strings.

I would start with something like –

StreamTokenizer tokenizer = new StreamTokenizer(new BufferedReader(new FileReader("foo.in")));

while (tokenizer.nextToken() != StreamTokenizer.TT_EOF) {

                if (tokenizer.ttype == StreamTokenizer.TT_WORD)
                    // use tokenizer.sval
                else if (tokenizer.ttype == StreamTokenizer.TT_NUMBER)
                   // use tokenizer.nval
            }

Here is an example on how to use it. The above is a very common way for tokenizing files and reading char by char. You should of course use a FileReader or Buffer for performance reasons.

You can also use Scanner. Sample code would be like

Scanner s = new Scanner(file);
s.useDelimiter(""); // reads one char a time
while(s.hasNext()){
  if(s.hasNextInt(){
    // then do something with s.nextInt()
  }else{
    // then do something with s.next()
  }
}