» » How to check if first character of a string is a number or not in java

  • To check if first character of a string is a number or not in java we can check in multiple ways.
  • By using Character.isDigit() method by passing character of string using for loop or substring method.
  • Other way is to check str.substring(0, 1).matches("[0-9]").
  • Lets see an example program in java to check first character of a string is digit or character. 



Program #1: Java example program to check the each character of string is number or not   character is a letter or number in Java without using regexes?

  1. package StringInterviewprograms;
  2. /**
  3.  * Check whether the given character is a number /digit or not by using java character isdigit
  4.  *method
  5.  * @author www.instanceofjava.com
  6.  */
  7. public class CheckEachCharacterNumberOrNot {
  8.     public static void main(String[] args) {
  9.         String str = "instanceofjava37";
  10.  
  11.         //Check whether the given character is a number /digit or not ?
  12.  
  13.         for(int i=0; i<str.length();i++)
  14.         {
  15.             Boolean flag = Character.isDigit(str.charAt(i));
  16.  
  17.             if(flag){
  18.  
  19.                System.out.println("'"+str.charAt(i)+"' is a number");
  20.             }
  21.             else{
  22.                System.out.println("'"+str.charAt(i)+"' is not a number");
  23.             }
  24.  
  25.         }
  26.         
  27. }
  28.  
  29. }

Output:

  1. 'i' is not a number
  2. 'n' is not a number
  3. 's' is not a number
  4. 't' is not a number
  5. 'a' is not a number
  6. 'n' is not a number
  7. 'c' is not a number
  8. 'e' is not a number
  9. 'o' is not a number
  10. 'f' is not a number
  11. 'j' is not a number
  12. 'a' is not a number
  13. 'v' is not a number
  14. 'a' is not a number
  15. '3' is a number
  16. '7' is a number
     
Program #2: Java example program to check the First character of string is number or not by using regex.

  1. package StringInterviewprograms;
  2. /**
  3.  * Check whether the given character is a number /digit or not
  4.  * @author www.instanceofjava.com
  5.  */
  6. public class CheckFirstCharacterNumberOrNot {
  7.  
  8.     public static void main(String[] args) {
  9.         String str = "instanceofjava37";
  10.  
  11.           Boolean flag1 = str.substring(0, 1).matches("[0-9]");
  12.  
  13. if(flag1){
  14.  
  15.  System.out.println("First Character is a number..!");
  16.  
  17.  }
  18.  else{
  19.    System.out.println("First character is not a number..!");
  20. }
  21. }
  22.  
  23. }

Output:

  1. First character is not a number..!


Program #3: Java example program to check the First character of string is number or not using eclipse IDE.


Check first character string number digit java

Instance Of Java

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