How do I write simple character class regex?

A character class in the context of regular expression is a set of characters enclosed within a square brackets "[]". It specifies the characters that will successfully match a single character from the given input.

A simple class, the most basic form of character class, is formed simply by placing a set of characters side-by-side within square brackets. For example the regular expression b[ai]t will match the words "bit" or "bat" because the pattern defines a character class accepting either "i" or "a" as the middle character.

package org.kodejava.example.util.regex;

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

public class CharacterClassesSimpleClassDemo {
    public static void main(String[] args) {
        // Creating a simple class type of character classes.
        // The regular expression below will search all sequences
        // of string that begins with 'b', ends with 't' and have
        // a middle letter of 'a' or 'i'.
        String regex = "b[ai]t";

        // Compiles the pattern and obtains the matcher object.
        Pattern pattern = Pattern.compile(regex);
        Matcher matcher =
                pattern.matcher("I'm a little bit afraid of bats " +
                        "but not cats.");

        // Find every matches and prints it.
        while (matcher.find()) {
            System.out.format("Text "%s" found at %d to %d.%n",
          , matcher.start(), matcher.end());

The program will print the following output:

Text "bit" found at 13 to 16.
Text "bat" found at 27 to 30.

Wayan Saryada

Programmer, runner, recreational diver, currently living in the island of Bali, Indonesia. Mostly programming in Java, creating web based application with Spring Framework, Hibernate / JPA.

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