Special Characters like dot(.), hash(#), etc., which have a special meaning to the regular expression need to be escaped to match in the regular expression. For example, if dot(.) is not escaped in a regular expression, it matches any single character, thus giving ambiguous results.
Methods:
Characters can be escaped in Java Regex in two ways which are listed as follows which we will be discussing upto depth:
- Using \Q and \E for escaping
- Using backslash(\\) for escaping
Method 1: Using \Q and \E for escaping
- We can use the \Q and \E escape sequences to escape characters.
- \Q marks the start of the escape sequence whereas \E marks the end of the escape sequence.
- Any characters between the \Q and \E are escaped.
- Generally used for escaping multiple characters.
Implementation:
In the below source code the Regex pattern p is escaped for the dot(.) operator, whereas the pattern p1 is not escaped for dot(.). Thus, the pattern p matches only with the string s whereas the pattern p1 matches with both the strings s and s1.
Example
Java
// Java Program to Illustrate Escaping Characters in Java// Regex Using \Q and \E for escaping// Importing required classesimport java.io.*;import java.util.regex.*;// Main classclass GFG { // Main driver method public static void main(String[] args) { // Sample strings as inputs String s = "Geeks.forGeeks"; String s1 = "Lazyroar"; // Creating object of Pattern class // 1. Patterns with dot escaped Pattern p = Pattern.compile("\\Q.\\E"); // 2, Pattern without dot escaped Pattern p1 = Pattern.compile("."); // Matchers for each pattern string combination Matcher m = p.matcher(s); Matcher m1 = p.matcher(s1); Matcher m2 = p1.matcher(s); Matcher m3 = p1.matcher(s1); // Print and display whether p,p1 matches // or not via boolean true false System.out.println("p matches s: " + m.find()); System.out.println("p matches s1: " + m1.find()); System.out.println("p1 matches s: " + m2.find()); System.out.println("p1 matches s1: " + m3.find()); }} |
p matches s: true p matches s1: false p1 matches s: true p1 matches s1: true
Method 2: Using backslash(\\) for escaping
- We can use a backslash to escape characters.
- We require two backslashes as backslash is itself a character and needs to be escaped.
- Characters after \\ are escaped.
- It is generally used to escape characters at the end of the string.
Implementation:
In the below source code the Regex pattern p is escaped for the dot(.) operator, whereas the pattern p1 is not escaped for dot(.). Thus the pattern p matches only with the string s whereas the pattern p1 matches with both the strings s and s1.
Example:
Java
/*package whatever //do not write package name here */import java.io.*;import java.util.regex.*;class GFG { public static void main (String[] args) { String s="Geeks.forGeeks";//sample strings String s1="Lazyroar"; //patterns with dot escaped Pattern p=Pattern.compile("\\."); // pattern without dot escaped Pattern p1=Pattern.compile("."); //matchers for each pattern string combination Matcher m=p.matcher(s); Matcher m1=p.matcher(s1); Matcher m2=p1.matcher(s); Matcher m3=p1.matcher(s1); //outputs System.out.println("p matches s: "+m.find()); System.out.println("p matches s1: "+m1.find()); System.out.println("p1 matches s: "+m2.find()); System.out.println("p1 matches s1: "+m3.find()); }} |
Output:
p matches s: true p matches s1: false p1 matches s: true p1 matches s1: true