How to remove consonants from a string using regular expressions in Java?

The simple character class “[ ]” matches all the specified characters in it. The meta character ^ acts as negation within the above character class i.e. the following expression matches all the characters except b (including spaces and special characters)

"[^b]"

Similarly, the following expression matches all the consonants in the given input string.

"([^aeiouyAEIOUY0-9\W]+)";

Then you can remove the matched characters by replacing them with the empty string “”, using the replaceAll() method.

Example 1

public class RemovingConstants {
   public static void main( String args[] ) {
      String input = "Hi welc#ome to t$utori$alspoint";
      String regex = "([^aeiouAEIOU0-9\W]+)";
      String result = input.replaceAll(regex, "");
      System.out.println("Result: "+result);
   }
}

Output

Result: i e#oe o $uoi$aoi

Example 2

import java.util.Scanner;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
public class RemovingConsonants {
   public static void main( String args[] ) {
      Scanner sc = new Scanner(System.in);
      System.out.println("Enter input string: ");
      String input = sc.nextLine();
      String regex = "([^aeiouyAEIOUY0-9\W])";
      String constants = "";
      //Creating a pattern object
      Pattern pattern = Pattern.compile(regex);
      //Matching the compiled pattern in the String
      Matcher matcher = pattern.matcher(input);
      //Creating an empty string buffer
      StringBuffer sb = new StringBuffer();
      while (matcher.find()) {
         matcher.appendReplacement(sb, "");
      }
      matcher.appendTail(sb);
      System.out.println("Result: \n"+ sb.toString() );
   }
}

Output

Enter input string:
# Hello how are you welcome to Tutorialspoint #
Result:
# eo o ae you eoe o uoiaoi #