Regular expression or Regex is an API which is used for pattern matching and it basically defines a search pattern of input. We can also search, edit or manipulate text or data from regular expression. Let’s suppose if we need to define some constraints on any string(eg: passwords and email validation) then we will use regular-expression.
Benefit of regex:
1> Regex are fast for execution
2> Regex save time
3> Regex can match just about anything
4> Searching (and possibly replacing) text in files
Eg:Search pattern: (text)
The search pattern text will replace from replaced text in a file.
5> Renaming a hundred files at a time
Eg: Changing the File Extension:
Search pattern: ^(.*\.)[^.]+$
^(.*\.)[^.]--> Matches any character after the dot and then replace that string that is extension with rar.
Java Regex API provides 1 interface and 3 classes in java.util.regex package.