What is Regex and its implementation in Java

In this blog, we would discuss What is Regex and its implementation. Regular expressions are a powerful tool for matching patterns in strings. In many cases, you’ll want to match not just the characters in the string, but also the spaces between them. There are a few different ways to match whitespace in a regular expression. The most common is the \s character class, which includes all whitespace characters including space, tab, newline, and more.

 

 

If you want to be more specific, you can use the \t character class for tabs, the \r character class for carriage returns, and the character class for newlines. You can also match multiple consecutive whitespace characters with the \s+ character class. This is useful if you want to match more than one space, tab, or new line in a row. Finally, you can use the \b character class to match word boundaries. 

 

 

 

 

What are Regular Expressions

 

One of the most common uses for regular expressions is to find and replace text. This can be useful for removing extra whitespace from a document, or for replacing all instances of a certain word with another. To match whitespace with a regular expression, you can use the \s character class. This will match any whitespace character, including spaces, tabs, and newlines. If you want to match only specific types of whitespace, you can use the \t character class for tabs, the \r character class for carriage returns, and the character class for newlines. You can also use the \s character class to match multiple whitespace characters in a row. 

 

 

 

Examples of regex Whitespace 

 

There are many examples of Regex Whitespace in Java. Here are a few:

 

1. \s – matches a single whitespace character, including space, tab, form feed, etc.

 

2. \s+ – matches one or more whitespace characters, including space, tab, form feed, etc.

 

3. \s* – matches zero or more whitespace characters, including space, tab, form feed, etc.

 

4. \s? – matches zero or one whitespace character, including space, tab, form feed, etc.

 

5. \s{n} – matches exactly n whitespace characters, including space, tab, form feed, etc.

 

6. \s{n,} – matches at least n whitespace characters, including space, tab, form feed, etc.

 

7. \s{n,m} – matches at least n but not more than m whitespace characters, including space, tab, form feed, etc.

 

 

 

 

Implementation of Regex 

 

There are many ways for the implementation of regex in Java. One common way is to use the java.util.regex package. This package provides the class Pattern, which represents a compiled regular expression, and the class Matcher, which matches a given regular expression against an input string. The Pattern class provides several static methods for compiling regular expressions.

 

The most common one is probably Pattern.compile(String regex).

 

 

This method takes a regular expression as a string and compiles it into a Pattern object. Once you have a Pattern object, you can use it to create a Matcher object by calling the matcher(String input) method. The Matcher class has a number of methods for matching a regular expression against an input string.

 

 

The most common one is probably find(), which tries to find the next substring that matches the regular expression. If it finds a match, it returns true and sets the matcher’s start and end indices to the boundaries of the match. You can then use the group() method to get the matched substring.

 

 

The regex whitespace is represented by the \s character class. To match a whitespace character, we use the \s in the regular expression. For example, the following code matches the space, tab, newline, and carriage return characters.

 

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

public class abhi {

public static void main(String[] args)
{ // Define the regex pattern 

        String input = "This is a test.";
        String regex = "\\s"; 
        Pattern pattern = Pattern.compile(regex); 
        Matcher matcher = pattern.matcher(input);
        boolean matchFound = matcher.find(); // Prints true 
        System.out.println(matchFound);
        
        } 
}
    

 

Output

 

 

 

The above code prints true as the input string contains whitespace characters.

 

 

We can also use the regex whitespace to match the non-whitespace characters. To do this, we use the \S character class. The \S is the negated form of \s. It matches any character that is not a whitespace character. For example,

 

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

public class abhi {

public static void main(String[] args)
{ // Define the regex pattern 

    String input = "This is a test."; 
    String regex = "\\S"; 
    Pattern pattern = Pattern.compile(regex); 
    Matcher matcher = pattern.matcher(input); 
    boolean matchFound = matcher.find();  
    System.out.println(matchFound);
        
        } 
}

 

Output

 

 

 

The above code prints true as the input string contains non-whitespace characters.

 

 

We can also use the regex whitespace to match the empty string. The empty string is a string that contains no characters. To match the empty string, we use the ^$ regular expression. For example,

 

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

public class abhi {

public static void main(String[] args)
{ // Define the regex pattern 

    String input = ""; 
    String regex = "^$"; 
    Pattern pattern = Pattern.compile(regex); 
    Matcher matcher = pattern.matcher(input); 
    boolean matchFound = matcher.find();  
    System.out.println(matchFound);
        
        } 
}

 

Output

 

 

 

The above code prints true as the input string is empty.

 

 

We can also use the regex whitespace to match the strings that end with whitespace characters. To do this, we use the \\s$ regular expression. For example,

 

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

public class abhi {

public static void main(String[] args)
{ // Define the regex pattern 

    String input = "This is a test. "; 
    String regex = "\\s$";
    Pattern pattern = Pattern.compile(regex); 
    Matcher matcher = pattern.matcher(input); 
    boolean matchFound = matcher.find();  
    System.out.println(matchFound);
        
        } 
}

 

Output

 

The above code prints true as the input string ends with a whitespace character.

 

 

Also, read – The Complete Manual for the GPT-3 Language Model