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 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.");
  }
}