Definition of regular expression

Regular Expression in compiler construction | T4Tutorials.com

RegEx practice/tutorial

Java - Replace each substring in a string, matches the regexp

SOLVED: In Java, write a class named Password with a String field and a constructor that accepts a String object as its argument and sets the String field. The class should have a method named isValidCount that returns true if the number of 'a', 'b', and 'c' in the String field is at least 4, otherwise returns false.

Linux Regular Expression Tutorial: Grep Regex Example