Question

I have a flat file like:

A 10
S 20
W A 20 10
S A 45 10
S W S 20 20 20 30
W A S 22 50 20 55

I want to make sure it is well formed, (separated by blank space ” “)
allowing only a regular expression like:

anyword* then " " then (word*|numbers*)*

where * is any number of words
but there is also one issue,

• if there is only one word or char there is only one number
• if there are 2 words or chars separated by ” ” then there must be 2 numbers separated by ” “
• if there are 3 words or chars separated by ” ” then there must be 4 numbers separated by ” “

I was doing something like this, but do not know where to incorporate validation of line

try {
      input = new BufferedReader(new FileReader(new File(filename)));
      String line = null;
      while ((line = input.readLine()) != null) {
           String[] words = line.split(" ");
       if (words.length == 2) {

           }
     }  
 }

Answer 1

This regex should do it:

^[a-z]+ (?:\d+|[a-z]+(?: \d+ \d+| [a-z]+(?: \d+){4}))$

I tried to make it as short as possible, but it may be possible to condense it a bit more. This should be used with case sensitivity enabled or you should change all of the [a-z] to [a-zA-Z].

Here is a Rubular.