How to parse numbers from a string using regex

Question

I'm trying to understand why my regex below is failing. I'm trying to retrieve a range of values on both sides of the : but my code always fails to the else . range is coming from a command line arg like this java -jar myprogram.jar -R 50:100 .

Is it failing because I'm passing a string to the matches() and looking for integers?

Here is my code:

private int[] parseRangeResults(String range) {
   int[] rangeResults = new int[2];

   if(range.matches("\\d+:\\d+")) {

      String[] numbers = range.split(":")
      rangeResults[0] = Integer.parseInt(numbers[0]);
      rangeResults[1] = Integer.parseInt(numbers[1]);
   } else {
      throw new Exception("Invalid Syntax.");
   }
   return rangeResults;
}   

Answer 1

I would write it like this

private static int[] parseRangeResults(String range) {
    String[] numbers = range.split(":", -2)
    return new int[] {Integer.parseInt(numbers[0]),Integer.parseInt(numbers[1])};
}

If there is no : it will give you an IndexOutOfBoundException: 1

If there is an invalid number like 1abc:234 you will get NumberFormatException: Unable to parse 1abc

Answer 2

The issue is your handling of the output array. String.split removes the delimiter and does not include it in the array. Your numbers will be in numbers[0] and numbers[1] . numbers[2] will throw an exception.

Answer 3

private int[] parseRangeResults(String range) {
   int[] rangeResults = new int[2];
   if(range.matches("\\d+:\\d+")) {   
      String[] numbers = range.split(":")
      rangeResults[0] = Integer.parseInt(numbers[0]);
      rangeResults[1] = Integer.parseInt(numbers[1]);
   } else {
      throw new Exception("Invalid Syntax.");
   }
   return rangeResults;
}

Answer 4

Regex "\\\\d+:\\\\d+" for string "asdf123:456qwerty" will always return true

Use that regex instead

"^\\d+:\\d+$"

Or use exceptions

try{
    Integer.parseInt("asdf");
}catch(NumberFormatException e){
    throw ...;
}

And

try{
    String s1 = p[0];
    String s2 = p[1];
}catch(ArrayIndexOutOfBoundsException e){
    throw ...;
}

PS. Are you sure about numbers[2] ?