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Understanding Regular Expressions: Key Concepts and Java Implementation

In this lecture, we explore Chapter 5 on Regular Expressions, a crucial topic in web site construction and management. We will review patterns, wildcards, special characters, and escape sequences essential for string matching. Important topics include character classes, predefined classes, alternation, and grouping and capturing techniques. Additionally, we'll discuss the upcoming mid-term on June 21st, covering chapters 1-4, and options for extra credit. Essential for any Java programmer, this lecture will prepare you for practical applications of regex in your coding tasks.

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Understanding Regular Expressions: Key Concepts and Java Implementation

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  1. CGS – 4854 Summer 2012 Instructor: Francisco R. Ortega Chapter 5 Regular Expressions Web Site Construction and Management

  2. Today’s Lecture • Chapter 5 Regular Expressions • Talk about tutorial 4 and homework 4 • Help with homework #4

  3. Mid-Term • Mid-Term June 21st. • Chapters 1,2,3 and 4. • Possible review for mid-term • June 14 (after quiz 4) or June 19 • Extra Credit for Mid-Term • Extra credit question may be Java related or Regular Expressions (if covered before the exam) • You are allowed to bring one letter size paper to the exam

  4. ASCII Table (Part 1)

  5. Regular Expressions • Match strings of text (wiki) • Sequence of regular expressions is known as a pattern • Regular expressions contain • Wildcards • Special characters • Escape sequences

  6. Regular Expressions 101 • Characters match themselves except: [\^$.|?*+() • \ suppresses the meaning of special characters • [] starts a character class. We match one from the class. • - specifies a range of characters • ^ negates a character class • . matches any single character except line break • | matches either the left, or the right (or)

  7. Character Classes • [xyz] : will match x or y or z • [a-z] : will match lowercase letters • [a-zA-Z] : will match all letters • [a-Z] :will not match any letters (why?) • [A-z] : will match all letters but additional symbols. Why? • [^abc] : Any character except for a,b or c.

  8. Predefined classes

  9. Escape Sequence • \. : would match a period • [.] : would match a period • \ does not lose special meaning inside square brackets [\d]

  10. Alternation • yes|no • yes|no|maybe • It will match either yes,no or maybae. • But only one of them.

  11. Grouping and Capturing • (pattern) • Capturing pattern. • Can retrieve values from \1 thru \9 • Example • Text: abyes3 • [a-z] ([a-z]) (yes|no) \d • \1 is equal to b • \2 is equal to yes • (?:pattern) • Only used for grouping

  12. Ignoring case • (?i)yes|no • [yY] [eE] [sS] | [Nn] [Oo]

  13. Repetition

  14. Regex in java • You will need to use two backslashes • Regex: \d • Java regex: “\\d”

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