Regex Special Characters in Java

1. Special Characters in Java Regular Expressions
2. Example of Using Regex Special Characters in Java

Regex (Regular Expression) is a useful tool for manipulating, searching, and processing text strings. It simplifies and reduces the number of lines in a program.

We’ll look at how special characters are utilized in regex.

Special Characters in Java Regular Expressions

Regex is a type of textual syntax representing patterns for text matching. Regular expressions make use of special characters such as ., +, *, ?, ^, $, (, ), [, ], {, }, |, \.

Characters in a regular expression (those in the string representing its pattern) are either metacharacters with a special meaning or regular characters with a literal meaning.

Example of Using Regex Special Characters in Java

In this example, we used the Pattern and Matcher classes from the java.util.regex package. The Pattern class represents a regular expression.

When we create an instance of the Pattern class, we pass the regular expression as a string.

Here we have a regular expression regex_pattern as a String. This pattern is used to check if a password meets the following criteria.

1. At least one digit [0-9] must be included in the password.
2. At least one lowercase character [a-z] is required in the password.
3. At least one uppercase character [A-Z] is required in the password.
4. At least one special character, such as ! @ # & (), must be included in the password.
5. A password must be at least 8 characters long and no more than 24 characters long.

The compile() method creates a pattern from the specified regular expression. We’ll use this pattern to make a Matcher object later.

This pattern can be matched with any character sequence against the regular expression using the Matcher object. The matcher method creates a matcher that matches the given input against the pattern.

We match two strings to the pattern and print the output (a Boolean returned by the matches() method).

import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class RegexTest {
    public static void main(String [] args) {
        String regex_pattern =
                "^(?=.*[0-9])(?=.*[a-z])(?=.*[A-Z])(?=.*[!@#&()–[{}]:;',?/*~$^+=<>]).{8,24}$";

        Pattern pattern = Pattern.compile(regex_pattern);

        String inputPassword1 = "Password1@@1990";
        String inputPassword2 = "Pass190";

        Matcher matcher1 = pattern.matcher(inputPassword1);
        Matcher matcher2 = pattern.matcher(inputPassword2);

        System.out.println("Password 1 matches pattern : "+matcher1.matches());
        System.out.println("Password 2 matches pattern : "+matcher2.matches());

    }
}

Output:

Password 1 matches pattern : true
Password 2 matches pattern : false