Java Program to Illustrate Escaping Characters in Regex

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The special characters, also known as metacharacters, in Java Regex holds a specific meaning within the regex syntax and must be escaped if you want to use them as regular characters.

Here, we will demonstrate escaping characters in Regex through Java Program. But, before diving deep into the topic, let us get familiar with the term Regex in Java.

What is Regex?

It is an acronym for a Regular expression. It is an API that offers users to define String patterns that are useful for finding, modifying, and editing strings. A couple of areas of strings where Regex is frequently used to define the limitations include email validation and passwords. The java.util.regex package encompasses regular expressions.

Escaping Characters in Regex using \Q and \E

To escape characters, we can use the Q and E escape sequences, which begin with the letter Q and end with the letter E. All characters will be escaped between the letters Q and E.

Suppose you want to escape the String "Java", put this string within the \Q and \E as shown below −

\Qjava\E

Example

The following Java program demonstrates how to escape dot(.) in regex.

// Java Program to demonstrate how to escape characters in Java
// Regex Using \Q and \E for escaping

import java.io.*;
import java.util.regex.*;
//creation of a class named Regexeg1
public class Regexeg1 {
   // Main method
   public static void main(String[] args) {
      // providing two strings as inputs
      String s1 = "Tutorials.point";
      String s2 = "Tutorialspoint";
      //creation of an object of Pattern class with dot escaped
      Pattern p1 = Pattern.compile("\\Q.\\E");
      //creation of an object of Pattern class without escaping the dot
      Pattern p2 = Pattern.compile(".");
      // Matchers for every combination of patterns and strings
      Matcher m1 = p1.matcher(s1);
      Matcher m2 = p1.matcher(s2);
      Matcher m3 = p2.matcher(s1);
      Matcher m4 = p2.matcher(s2);
      // find whether p1 and p2 match and display the Boolean value as a result
      System.out.println("p1 matches s1: " + m1.find());
      System.out.println("p1 matches s2: " + m2.find());
      System.out.println("p2 matches s1: " + m3.find());
      System.out.println("p2 matches s2: " + m4.find());
   }
}

Output obtained as −

p1 matches s1: true
p1 matches s2: false
p2 matches s1: true
p2 matches s2: true

Escaping Characters in Regex using Backslash

The primary method to escape special characters in Java regular expression is by using the backslash. However, since the backslash is also an escape character in Java strings, you need to use double backslashes (\) in your regex patterns.

For example, to match the string "java.util.regex", your regex pattern would be −

java\.util\.regex

The above pattern will treat the dot, which is a special character in regular expression, as a simple dot.

Example

The following Java program illustrates how to escape character in regex using backslash.

// Java Program to demonstrate how to escape characters in Java
// Regex using backslash (\) for escaping
import java.util.regex.*;
public class Regexeg2 {
   public static void main(String[] args) {
      // creating string and a regex pattern
      String text1 = "java.util.regex";
      String regex1 = "java\\.util\\.regex";
      // checking matches
      System.out.println("Both String Matched: " + text1.matches(regex1));
   }
}

Output of the above code is −

Both String Matched: true