Posix character classes p{Digit} Java regex

In this article, we will learn about the POSIX character classes p{Digit} Java regex. First, will know about \p{Digit} and the use of \p{Digit} along with examples.

What is \p{Digit}?

In Java regex, the \p{Digit} is a POSIX (Portable Operating System Interface) character class in Java regular expressions that matches any decimal digit character. This class matches decimal digits from 0 to 9. 

The \p{Digit} is also equivalent to other expressions in Java:

• "\d": Follows the same POSIX standards.
• "[0-9]": For ASCII digits only.

How to Use \p{Digit} in Java?

We can use the \p{Digit} POSIX character in Java by declaring it in a string literal. In Java string literals, you need to escape the backslash with another backslash.

Below is the basic syntax for using \p{Digit} in Java regular expressions:

String regex = "[\p{Digit}]";

Example 1

Below is an example to count the number of digits present in a string using the \p{Digit} in Java1:

import java.util.Scanner;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
public class DigitsExample {
   public static void main(String args[]) {
      //Reading String from user
      System.out.println("Enter a string");
      Scanner sc = new Scanner(System.in);
      String input = sc.nextLine();
      //Regular expression
      String regex = "[\p{Digit}]";
      //Compiling the regular expression
      Pattern pattern = Pattern.compile(regex);
      //Retrieving the matcher object
      Matcher matcher = pattern.matcher(input);
      int count = 0;
      while(matcher.find()) {
         count++;
      }
      System.out.println("Number of digits: "+count);
   }
}

Output

Enter a string
sample text 22 37 48 84
Number of digits: 8

Enter a string 
Welcome to tutorilspoint 
Number of digits: 0

Example 2

Below is an example to print strings with only digits from a list of 5 strings using the \p{Digit} in Java:

import java.util.Scanner;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
public class Example {
   public static void main( String args[] ) {
      //Regular expression to match lower case letters
      String regex = "^\p{Digit}+$";
      //Getting the input data
      Scanner sc = new Scanner(System.in);
      System.out.println("Enter 5 input strings: ");
      String input[] = new String[5];
      for (int i=0; i<5; i++) {
         input[i] = sc.nextLine();
      }
      //Creating a Pattern object
      Pattern p = Pattern.compile(regex);
      System.out.println("Strings with only digits: ");
      for(int i=0; i<5;i++) {
         //Creating a Matcher object
         Matcher m = p.matcher(input[i]);
         if(m.matches()) {
            System.out.println(m.group());
         }
      }
   }
}

Output

Enter 5 input strings:
hello
1234
243test
##$$@
222356
Strings with only digits:
1234
222356