Java - Regular Expressions Part 2: Core Regex Syntax and Metacharacters

Metacharacters:

.: Matches any character except a newline.

^ and $: Anchor the match at the start or end of the string.

[]: Matches any character in the set.

Example 1: Dot Metacharacter

String pattern = ".ar";

String text = "car";

System.out.println(text.matches(pattern)); // true

Example 2: Anchors

String pattern = "^hello";

String text = "hello world";

System.out.println(text.matches(pattern + ".*")); // true

Example 3: Character Set

String pattern = "[aeiou]";

String text = "hello";

System.out.println(text.matches(".*" + pattern + ".*")); // true

Example 4: Quantifiers

*: Matches 0 or more times.

+: Matches 1 or more times.

{n}: Matches exactly n times.

String pattern = "a+b*";

System.out.println("aaab".matches(pattern)); // true

System.out.println("b".matches(pattern));    // false