Java Buzz Forum - 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?

package StringInterviewprograms;
/**
* Check whether the given character is a number /digit or not by using java character isdigit
*method
* @author www.instanceofjava.com
*/
public class CheckEachCharacterNumberOrNot {
public static void main(String[] args) {
String str = "instanceofjava37";
//Check whether the given character is a number /digit or not ?
for(int i=0; i<str.length();i++)
{
Boolean flag = Character.isDigit(str.charAt(i));
if(flag){
System.out.println("'"+str.charAt(i)+"' is a number");
}
else{
System.out.println("'"+str.charAt(i)+"' is not a number");
}
}
}
}

Output:

'i' is not a number
'n' is not a number
's' is not a number
't' is not a number
'a' is not a number
'n' is not a number
'c' is not a number
'e' is not a number
'o' is not a number
'f' is not a number
'j' is not a number
'a' is not a number
'v' is not a number
'a' is not a number
'3' is a number
'7' is a number

Program #2: Java example program to check the First character of string is number or not by using regex.

package StringInterviewprograms;
/**
* Check whether the given character is a number /digit or not
* @author www.instanceofjava.com
*/
public class CheckFirstCharacterNumberOrNot {
public static void main(String[] args) {
String str = "instanceofjava37";
Boolean flag1 = str.substring(0, 1).matches("[0-9]");
if(flag1){
System.out.println("First Character is a number..!");
}
else{
System.out.println("First character is not a number..!");
}
}
}

Output:

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


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