Best implementation for an isNumber(string) method

Question

In my limited experience, I\'ve been on several projects that have had some sort of string utility class with methods to determine if a given string is a number. The idea h

Answer 1

I use this but I liked Asaph's rigor in his post.

public static bool IsNumeric(object expression)
{
if (expression == null)
return false;

double number;
return Double.TryParse(Convert.ToString(expression, CultureInfo.InvariantCulture),   NumberStyles.Any,
NumberFormatInfo.InvariantInfo, out number);
}

Answer 2

 public static boolean isNumber(String str){
      return str.matches("[0-9]*\\.[0-9]+");
    }

to check whether number (including float, integer) or not

Answer 3

I like code:

public static boolean isIntegerRegex(String str) {
    return str.matches("^[0-9]+$");
}

But it will good more when create Pattern before use it:

public static Pattern patternInteger = Pattern.compile("^[0-9]+$");
public static boolean isIntegerRegex(String str) {
  return patternInteger.matcher(str).matches();
}

Apply by test we have result:

This operation isIntegerParseInt took 1313 ms.
This operation isIntegerRegex took 1178 ms.
This operation isIntegerRegexNew took 304 ms.

With:

public class IsIntegerPerformanceTest {
  private static Pattern pattern = Pattern.compile("^[0-9]+$");

    public static boolean isIntegerParseInt(String str) {
    try {
      Integer.parseInt(str);
      return true;
    } catch (NumberFormatException nfe) {
    }
    return false;
  }

  public static boolean isIntegerRegexNew(String str) {
    return pattern.matcher(str).matches();
  }

  public static boolean isIntegerRegex(String str) {
    return str.matches("^[0-9]+$");
  }

    public static void main(String[] args) {
        long starttime, endtime;
    int iterations = 1000000;
    starttime = System.currentTimeMillis();
    for (int i = 0; i < iterations; i++) {
      isIntegerParseInt("123");
      isIntegerParseInt("not an int");
      isIntegerParseInt("-321");
    }
    endtime = System.currentTimeMillis();
    System.out.println("This operation isIntegerParseInt took " + (endtime - starttime) + " ms.");
    starttime = System.currentTimeMillis();
    for (int i = 0; i < iterations; i++) {
      isIntegerRegex("123");
      isIntegerRegex("not an int");
      isIntegerRegex("-321");
    }
    endtime = System.currentTimeMillis();
    System.out.println("This operation took isIntegerRegex " + (endtime - starttime) + " ms.");
    starttime = System.currentTimeMillis();
    for (int i = 0; i < iterations; i++) {
      isIntegerRegexNew("123");
      isIntegerRegexNew("not an int");
      isIntegerRegexNew("-321");
    }
    endtime = System.currentTimeMillis();
    System.out.println("This operation took isIntegerRegexNew " + (endtime - starttime) + " ms.");
  }
}

Answer 4

You could create an extension method for a string, and make the whole process look cleaner...

public static bool IsInt(this string str)
{
    int i;
    return int.TryParse(str, out i);
}

You could then do the following in your actual code...

if(myString.IsInt())....

Answer 5

I think people here is missing a point. The use of the same pattern repeatedly has a very easy optimization. Just use a singleton of the pattern. Doing it, in all my tests the try-catch approach never have a better benchmark than the pattern approach. With a success test try-catch takes twice the time, with a fail test it's 6 times slower.

public static final Pattern INT_PATTERN= Pattern.compile("^-?[0-9]+(\\.[0-9]+)?$");

public static boolean isInt(String s){
  return INT_PATTERN.matcher(s).matches();
}

Answer 6

public static boolean CheckIfNumber(String number){

    for(int i = 0; i < number.length(); i++){
        try{
            Double.parseDouble(number.substring(i));

        }catch(NumberFormatException ex){
            return false;
        }
    }
    return true;     
}

I had this problem before but when I had input a number and then a character, it would still return true, I think this is the better way to do it. Just check if every char is a number. A little longer but it takes care if you have the situation of a user inputting "1abc". For some reason, when I tried to try and catch without iterating, it still thought it was a number so..