Java Regex

Java Regex

The Java Regex or Regular Expression is an API that defines a pattern for searching or manipulating strings.

It is widely used to define the constraint strings such as password and email validation.

The Matcher and Pattern classes provide the facility of Java regular expression. The java.util.regex package provides the following classes and interfaces for regular expressions.

• 1.   MatchResult interface
• 2.   Matcher class
• 3.   Pattern class
• 4.   PatternSyntaxException class

 

Regex Character classes

No.	Character Class	Description
1	[abc]	a, b, or c (simple class)
2	[^abc]	Any character except a, b, or c (negation)
3	[a-zA-Z]	a through z or A through Z, inclusive (range)
4	[a-d[m-p]]	a through d, or m through p: [a-dm-p] (union)
5	[a-z&&[def]]	d, e, or f (intersection)
6	[a-z&&[^bc]]	a through z, except for b and c: [ad-z] (subtraction)
7	[a-z&&[^m-p]]	a through z, and not m through p: [a-lq-z](subtraction)

Regex Quantifiers

The quantifiers specify the number of occurrences of a character.

Regex Description

X?	X occurs once or not at all
X+	X occurs once or more times
X*	X occurs zero or more times
X{n}	X occurs n times only
X{n,}	X occurs n or more times
X{y,z}	X occurs at least y times but less than z times

Regex Metacharacters

The regular expression metacharacters work as shortcodes.

Regex Description

.	Any character (may or may not match terminator)
\d	Any digits, short of [0-9]
\D	Any non-digit, short for [^0-9]
\s	Any whitespace character, short for [\t\n\x0B\f\r]
\S	Any non-whitespace character, short for [^\s]
\w	Any word character, short for [a-zA-Z_0-9]
\W	Any non-word character, short for [^\w]
\b	A word boundary
\B	A non-word boundary

Example 1:

package String;

import java.util.regex.Matcher;

import java.util.regex.Pattern;

public class RegexExample {

public static void main(String[] args) {

// Input text containing phone numbers

String inputText = "John: 123-456-7890, Jane: 987-654-3210, Bob: 555-1234";

// Define a regex pattern for matching phone numbers

String phoneRegex = "\\b\\d{3}-\\d{3}-\\d{4}\\b";

// Create a Pattern object

Pattern phonePattern = Pattern.compile(phoneRegex);

// Create a Matcher object

Matcher matcher = phonePattern.matcher(inputText);

// Find and print all matching phone numbers

System.out.println("Matching phone numbers:");

while (matcher.find()) {

System.out.println(matcher.group());

}

// Extract area codes from phone numbers using capturing groups

String areaCodeRegex = "\\b(\\d{3})-\\d{3}-\\d{4}\\b";

Pattern areaCodePattern = Pattern.compile(areaCodeRegex);

Matcher areaCodeMatcher = areaCodePattern.matcher(inputText);

// Find and print all area codes

System.out.println("\nExtracted area codes:");

while (areaCodeMatcher.find()) {

System.out.println("Area Code: " + areaCodeMatcher.group(1));

}

}

}

Example 2:

package String;

import java.util.regex.*;

public class RegexExample2 {

public static void main(String[] args) {

Pattern pat = Pattern.compile(" .m");

Matcher mat = pat.matcher(" .am");

Boolean bool = mat.matches();

System.out.println(bool); //return whether the pattern matches/not

Boolean bool1 = Pattern.matches(" .m", " .am");

System.out.println(bool1);

System.out.println(Pattern.matches("[amn]", "acd"));

System.out.println(Pattern.matches("[^amn]", "c"));

System.out.println(Pattern.matches("[a-zA-S]", "T"));

System.out.println(Pattern.matches("[MS][a-z]{5}", "Monica"));

System.out.println(Pattern.matches("[xyz]?", "x"));

System.out.println(Pattern.matches("[xyz]+", "x"));

System.out.println(Pattern.matches("[xyz]*", "xyyza"));

System.out.println(Pattern.matches("[\\d]", "1"));

System.out.println(Pattern.matches("[\\D]", "1"));

}

}