[java] How to check that a string is parseable to a double?

Is there a native way (preferably without implementing your own method) to check that a string is parseable with Double.parseDouble()?

You can always wrap Double.parseDouble() in a try catch block.

try
{
  Double.parseDouble(number);
}
catch(NumberFormatException e)
{
  //not a double
}

All answers are OK, depending on how academic you want to be. If you wish to follow the Java specifications accurately, use the following:

private static final Pattern DOUBLE_PATTERN = Pattern.compile(
    "[\\x00-\\x20]*[+-]?(NaN|Infinity|((((\\p{Digit}+)(\\.)?((\\p{Digit}+)?)" +
    "([eE][+-]?(\\p{Digit}+))?)|(\\.((\\p{Digit}+))([eE][+-]?(\\p{Digit}+))?)|" +
    "(((0[xX](\\p{XDigit}+)(\\.)?)|(0[xX](\\p{XDigit}+)?(\\.)(\\p{XDigit}+)))" +
    "[pP][+-]?(\\p{Digit}+)))[fFdD]?))[\\x00-\\x20]*");

public static boolean isFloat(String s)
{
    return DOUBLE_PATTERN.matcher(s).matches();
}

This code is based on the JavaDocs at Double.

Something like below should suffice :-

String decimalPattern = "([0-9]*)\\.([0-9]*)";  
String number="20.00";  
boolean match = Pattern.matches(decimalPattern, number);
System.out.println(match); //if true then decimal else not  

Google's Guava library provides a nice helper method to do this: Doubles.tryParse(String). You use it like Double.parseDouble but it returns null rather than throwing an exception if the string does not parse to a double.

Apache, as usual, has a good answer from Apache Commons-Lang in the form of NumberUtils.isCreatable(String).

Handles nulls, no try/catch block required.