Regular expressions are very strong but expensive tool. It is valid to use them for checking if the first character is a digit but it is not so elegant :) I prefer this way:
public boolean isLeadingDigit(final String value){
final char c = value.charAt(0);
return (c >= '0' && c <= '9');
}
I just came across this question and thought on contributing with a solution that does not use regex.
In my case I use a helper method:
public boolean notNumber(String input){
boolean notNumber = false;
try {
// must not start with a number
@SuppressWarnings("unused")
double checker = Double.valueOf(input.substring(0,1));
}
catch (Exception e) {
notNumber = true;
}
return notNumber;
}
Probably an overkill, but I try to avoid regex whenever I can.
To verify only first letter is number or character -- For number Character.isDigit(str.charAt(0)) --return true
For character Character.isLetter(str.charAt(0)) --return true
IN KOTLIN :
Suppose that you have a String
like this :
private val phoneNumber="9121111111"
At first you should get the first one :
val firstChar=phoneNumber.slice(0..0)
At second you can check the first char
that return
a Boolean
:
firstChar.isInt() // or isFloat()
regular expression starts with number->'^[0-9]'
Pattern pattern = Pattern.compile('^[0-9]');
Matcher matcher = pattern.matcher(String);
if(matcher.find()){
System.out.println("true");
}
Source: Stackoverflow.com