Check if a String is numeric in Java

0 votes
Check a String if it is a number before we parse the string.
Apr 16, 2018 in Java by Parth
• 4,630 points
3,426 views

3 answers to this question.

0 votes
  1. With Apache Commons Lang 3.4 and below: NumberUtils.isNumber or StringUtils.isNumeric.
  2. While using Apache Commons Lang 3.5 and above: NumberUtils.isCreatable or StringUtils.isNumeric.
  3. You can also use StringUtils.isNumericSpace which returns true for empty strings and ignores internal spaces in the string
Hope this helps!
Check out the Java Course and learn more about Java strings.
Thanks!
answered Apr 16, 2018 by developer_1
• 3,320 points
0 votes

This is the fastest way i know to check if String is Number or not:

public static boolean isNumber(String str){
  int i=0, len=str.length();
  boolean a=false,b=false,c=false, d=false;
  if(i<len && (str.charAt(i)=='+' || str.charAt(i)=='-')) i++;
  while( i<len && isDigit(str.charAt(i)) ){ i++; a=true; }
  if(i<len && (str.charAt(i)=='.')) i++;
  while( i<len && isDigit(str.charAt(i)) ){ i++; b=true; }
  if(i<len && (str.charAt(i)=='e' || str.charAt(i)=='E') && (a || b)){ i++; c=true; }
  if(i<len && (str.charAt(i)=='+' || str.charAt(i)=='-') && c) i++;
  while( i<len && isDigit(str.charAt(i)) ){ i++; d=true;}
  return i==len && (a||b) && (!c || (c && d));
}
static boolean isDigit(char c){
  return c=='0' || c=='1' || c=='2' || c=='3' || c=='4' || c=='5' || c=='6' || c=='7' || c=='8' || c=='9';
}
answered Aug 2, 2018 by samarth295
• 2,220 points
0 votes

Java 8 Lambda Expression is used:

String someString = "123123";
boolean isNumeric = someString.chars().allMatch( Character::isDigit );
answered Sep 3, 2018 by Daisy
• 8,120 points

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