Regex – Match Any Character(s)

In regular expressions, we can match any character using period "." character. To match multiple characters or a given set of characters, we should use character classes.

1. Matching a Single Character Using Regex

By default, the '.' dot character in a regular expression matches a single character without regard to what character it is. The matched character can be an alphabet, a number or, any special character.

To create more meaningful patterns, we can combine the dot character with other regular expression constructs.

. (Dot)Matches only a single character.
A.BMatches only a single character at second place in a 3 character long string where the string starts with ‘A’ and ends with ‘B’.
[abc]Matches only a single character from a set of given characters.
[aA] Matches only a single character ‘a’, case-insensitive.
import java.util.regex.Pattern;

public class Main {
    public static void main(String[] args)
        Pattern.compile(".").matcher("a").matches();    //true
        Pattern.compile(".").matcher("ab").matches();   //false

        Pattern.compile("A.B").matcher("AIB").matches();    //true
        Pattern.compile("A.B").matcher("ABI").matches();    //false

        Pattern.compile("A[abc]B").matcher("AaB").matches();    //true
        Pattern.compile("A[abc]B").matcher("AkB").matches();    //false

2. Matching Range of Characters

If we want to match a range of characters at any place, we need to use character classes with a hyphen between the range. e.g. ‘[a-f]’ will match a single character which can be either of ‘a’, ‘b’, ‘c’, ‘d’, ‘e’ or ‘f’.

[a-f]Matches only a single character in the range from ‘a’ to ‘f’.
[a-z]Matches only a single lowercase character in the range from ‘a’ to ‘z’.
[A-Z]Matches only a single uppercase character in the range from ‘A’ to ‘Z’.
[a-zA-Z]Matches only a single character in the range from ‘a’ to ‘z’, case-insensitive.
[0-9]Matches only a single number in the range from ‘0’ to ‘9’.
import java.util.regex.Pattern;

public class Main
	public static void main(String[] args)
		System.out.println(Pattern.compile("[a-f]").matcher("b").matches());	//true
		System.out.println(Pattern.compile("[a-f]").matcher("g").matches());	//false

		System.out.println(Pattern.compile("[a-zA-Z]").matcher("a").matches());	//true
		System.out.println(Pattern.compile("[a-zA-Z]").matcher("B").matches());	//true
		System.out.println(Pattern.compile("[a-zA-Z]").matcher("4").matches());	//false

		System.out.println(Pattern.compile("[0-9]").matcher("9").matches());	//true
		System.out.println(Pattern.compile("[0-9]").matcher("91").matches());	//false

3. Matching Multiple Characters

If we want to match a set of characters at any place then we need to use a wild card character ‘*‘ (asterisk) which matches 0 or more characters.

.*Matches any number of characters including special characters.
[0-9]*Matches any number of digits.
[a-zA-Z]* Matches any number of alphabets.
[a-zA-Z0-9]* Matches any number of alphanumeric characters.
Pattern.compile(".*").matcher("abcd").matches();                    //true
Pattern.compile("[a-zA-Z]*").matcher("abcd").matches();             //true
Pattern.compile("[0-9]*").matcher("01234").matches();               //true
Pattern.compile("[a-zA-Z0-9]*").matcher("a1b2c3").matches();       //true

Happy Learning !!

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