In Java, Regular Expressions $($regex$)$ are used in pattern matching with strings as well as for

validation of user input. Using these, a programmer can define search patterns for use in

text processing tasks. Some of the key constructs used to define them include syntax like

square brackets which represent a$($n$)$

quantifiers that specify how

often an element can appear and metacharacters. A few examples of useful java methods

to work with regex are the split$()$ method that divides the string around matches of the

given regex; Pattern.compile$()$ that compiles the given regex into a pattern, and

Matcher.find$()$ that scans through an input sequence looking for matches of this