Java regex check non-alphanumeric string

By mkyong | Updated: November 8, 2020

Viewed: 12,180 (+87 pv/w)

Tags: alphanumeric java regex regex string regex

The Alphanumericals are a combination of alphabetical [a-zA-Z] and numerical [0-9] characters, a total of 62 characters, and we can use regex [a-zA-Z0-9]+ to matches alphanumeric characters.

If we want regex matches non-alphanumeric characters, prefix it with a negate symbol ^, meaning we want any characters that are not alphanumeric.

  ^[^a-zA-Z0-9]+$

Regex explanation

  ^             # start string
  [^a-zA-Z0-9]  # NOT a-z, A-Z and 0-9
  +             # one or more
  $             # end string

1. Java regex non-alphanumeric

Below is a Java regex to check for non-alphanumeric characters.

package com.mkyong.regex.string;

public class StringNonAlphanumeric {

    public static void main(String[] args) {

        String str = "!@#$%";

        if (str.matches("^[^a-zA-Z0-9]+$")) {
            System.out.println("Yes, true.");
        } else {
            System.out.println("failed!");
        }
    }
}

Output

  Yes, true.

2. Java regex non-alphanumeric, underscore and colon

We can add all the invalid symbols into the bracket [ ].

  ^[^a-zA-Z0-9_:]+$

package com.mkyong.regex.string;

public class StringNonAlphanumericExtra {

    public static void main(String[] args) {

        String str = "!@#$%";

        if (str.matches("^[^a-zA-Z0-9_:]+$")) {
            System.out.println("Yes, true.");
        } else {
            System.out.println("failed!");
        }
    }
}

Output

  Yes, true.

For String str = "!@#_:";, now it will display below:

  failed!

Download Source Code

References

• Wikipedia – Alphanumericals
• Wikipedia – whitespace characters
• Java – How to remove spaces in between the String
• Java regex check alphanumeric string