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)

        Replace: $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: ^(.*\.)[^.]+$

       Replace: $1rar

^(.*\.)[^.]--> 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.

1. MatchResult interface

2. Matcher class

3. Pattern class

4. PatternSyntaxException class