RegEx handling in Java and the most important RegEx Patterns

RegEx.java

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

public class Main {
    public static void main(String[] args) {
        System.out.println("RegEx Demo");

        // The general java approach: Pattern, Matcher
        Pattern p = Pattern.compile("b(a|e)uer");
        Matcher m = p.matcher("bauer beuer");
        System.out.println(m.find());
        System.out.println(m.start());
        System.out.println(m.group());

        System.out.println(m.find());
        System.out.println(m.start());
        System.out.println(m.group());

        System.out.println(m.find());
//        System.out.println(m.start());
//        System.out.println(m.group());

        // Character classes
        System.out.println("\nCharacter Classes");
        p = Pattern.compile("b[ae]uer"); // same meaning as above
        m = p.matcher("bauer beuer");
        System.out.println(m.find());
        System.out.println(m.start());
        System.out.println(m.group());

        System.out.println(m.find());
        System.out.println(m.start());
        System.out.println(m.group());

        System.out.println("\nSimple identifier");
        p = Pattern.compile("^[A-Za-z][A-Za-z0-9]*$");
        m = p.matcher("127asfd");
        System.out.println(m.find());
//        System.out.println(m.start());
//        System.out.println(m.group());

        System.out.println("\nOptional Symbols");
        p = Pattern.compile("Ba(ue)?r");
        m = p.matcher("Bauer");
        System.out.println(m.find());
        System.out.println(m.start());
        System.out.println(m.group());

        System.out.println("\nMultiple occurrences");
        p = Pattern.compile("Baue+r");
        m = p.matcher("Baueeeeeeeeeeer");
        System.out.println(m.find());
        System.out.println(m.start());
        System.out.println(m.group());

        p = Pattern.compile("Baue{1,3}r");
        m = p.matcher("Bauer");
        System.out.println(m.find());
        System.out.println(m.start());
        System.out.println(m.group());

        System.out.println("\nPredefined char classes");
        p = Pattern.compile("Bau.r");
        m = p.matcher("Bau!r");
        System.out.println(m.find());
        System.out.println(m.start());
        System.out.println(m.group());

        // [0-9] == (\d)
        // \D not \d
        // white space (blank, tab, newline): \s
        // \S not \s
        // cheat sheet: https://www.petefreitag.com/cheatsheets/regex/
    }
}