1. Match Digits Using Character Class and Quantifier
This program uses the character class \d to match digits. The + quantifier matches one or more consecutive digits. It finds and displays all numbers present in the input.
import java.util.regex.*;
public class DigitCharacterClass {
public static void main(String[] args) {
String input = "Java 123 is released in 2026";
Pattern pattern = Pattern.compile("\\d+");
Matcher matcher = pattern.matcher(input);
while (matcher.find()) {
System.out.println("Matched: " + matcher.group());
}
}
}Output:
Matched: 123
Matched: 20262. Match Letters Using Character Class and Quantifier
This program uses [a-zA-Z] to match English alphabetic characters. The + quantifier matches one or more consecutive letters. It displays each word containing only alphabetic characters.
import java.util.regex.*;
public class LetterCharacterClass {
public static void main(String[] args) {
String input = "Java 123 Programming";
Pattern pattern = Pattern.compile("[a-zA-Z]+");
Matcher matcher = pattern.matcher(input);
while (matcher.find()) {
System.out.println("Matched: " + matcher.group());
}
}
}Output:
Matched: Java
Matched: Programming3. Match One or More Whitespace Characters
This program uses the \s character class to identify whitespace characters. The + quantifier matches one or more consecutive whitespace characters. It displays every whitespace sequence found in the input.
import java.util.regex.*;
public class WhitespaceCharacterClass {
public static void main(String[] args) {
String input = "Java Programming Language";
Pattern pattern = Pattern.compile("\\s+");
Matcher matcher = pattern.matcher(input);
while (matcher.find()) {
System.out.println("Matched whitespace: \"" + matcher.group() + "\"");
}
}
}Output:
Matched whitespace: " "
Matched whitespace: " "Code language: JavaScript (javascript)4. Match Specific Characters with a Quantifier
This program uses the character class [abc] to match a, b, or c. The {2,3} quantifier matches between two and three consecutive characters from this class. It displays all matching groups from the input.
import java.util.regex.*;
public class CharacterClassQuantifier {
public static void main(String[] args) {
String input = "ab abc abcd";
Pattern pattern = Pattern.compile("[abc]{2,3}");
Matcher matcher = pattern.matcher(input);
while (matcher.find()) {
System.out.println("Matched: " + matcher.group());
}
}
}Output:
Matched: ab
Matched: abc
Matched: abc