Regex Special Characters in Java

Rupam Yadav Feb 17, 2022
  1. Special Characters in Java Regular Expressions
  2. Example of Using Regex Special Characters in Java
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.

Metacharacter Use Example
^ start of the string or negation symbol ^a matches a at the start of the string
. matches any single character except the newline a.[0-9] matches a string that has an a followed by a character and a digit
[] Bracket expression that matches a single character contained within the brackets [a-c] equals to either a or b or c, i.e., a|b|c also [abc]
[^] matches a single character not contained in the brackets [^abc] matches any character other than a, b, or c
$ end of the line ^abc$ matches a string that starts and ends with abc
() grouping characters (ab)\1 matches abab
* Matches the preceding element or zero or more times ab*c matches ac, abc, abbbc, etc.
{m,n} Matches the preceding element at least m times and not more than n times a{3,5} matches aaa, aaaa, aaaaa
? Matches the preceding element zero or one time ab?c matches ac, abc
+ Matches the preceding element one or more times ab+c matches abc, abbc, abbbc, etc., but not ac
| the choice operator, it matches either the expression before or expression after the operator | ab|def matches either ab or def
\ Escape or backslash common escape sequences like \n or newline, \t for tab

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 =

        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());



Password 1 matches pattern : true
Password 2 matches pattern : false
Author: Rupam Yadav
Rupam Yadav avatar Rupam Yadav avatar

Rupam Saini is an android developer, who also works sometimes as a web developer., He likes to read books and write about various things.


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