Computer Programming

• Enumeration (enum)


  A data type that contains a fixed set of constants
• Enums are good to use when you already know all possibilities of the values or instances of the class
• Enums can be declared on their own or within another class
• With enums, it is impossible to create an invalid enum value without introducing a compiler error
• Examples of when enumerations are useful

  • Compass directions
  • Months of the year
  • Cards in a deck
• Creating an enum


  1. Declare a type with the enum keyword

  2. Provide an identifier for the type

  3. List the enum constants
• Enum constants


  • They are the only allowed values for the type
• Enum methods


  • toString()
  • ordinal()
  • equals()
  • compareTo()
• Static enum methods


  • valueOf()
  • values()
• Enums can be declared in their own file or within a class, but not within a method
• Enum usage in a switch statement

  • Displaying pizza prices based on size
• Using enums makes the values type-safe
• Nested classes


  Classes created within another class
• Types of nested classes

  • Static member class
  • Non-static member class (inner class)
  • Local class
  • Anonymous class
• Reasons for nesting classes

  • The inner class is used only by the top-level class
  • Packaging the classes together makes their connection easier to understand and their code easier to maintain
• Example of a nested class

  • RealEstateListing class with a nested HouseData class
• An inner class can access its top-level class's fields and methods, even if they are private, and an outer class can access its inner class's members
• Nested classes are not frequently created, but they are sometimes seen in built-in Java classes
• Regular expression (regex)


  A character or a sequence of characters that represent a string or multiple strings
• Regular expressions are part of the java.util.regex package
• Regular expressions


  • Allow for quicker, easier searching, parsing, and replacing of characters in a string
  • Are used to ensure that strings contain specific contents
  • Are often used to check correct email format (@ sign is included) on form validation
• String.matches(String regex)


  Returns true if a string matches the given regular expression
• Regex to check if animal is "cat" or "dog"

  • animal.matches("cat|dog")
• Regex to check if animal is "cat", "Cat", "dog", or "Dog"

  • animal.matches("[Cc]at|[Dd]og")
• Regex to check if word rhymes with "cat"


  • word.matches("[a-z]at")
• Regex to check if word starts with any letter and ends in "at"


  • word.matches("[a-zA-Z](at|AT)")
• Dot (.)


  Wildcard operator that represents any single character in regular expressions
• Repetition operators


  • * (0 or more occurrences)
  • ? (0 or 1 occurrence)
  • + (1 or more occurrences)
  • {x} (x occurrences)
  • {x,y} (between x & y occurrences)
  • {x,} (x or more occurrences)
• Regular expressions allow for very powerful validation of strings without having to write much code
• Pattern class


  Stores the format of a regular expression
• Matcher class


  Stores a possible match between a pattern and a string
• Using Pattern and Matcher

  1. Initialize pattern with Pattern.compile(regex)

  2. Initialize matcher with matcher = pattern.matcher(string)

  3. Use matcher.matches() to check if string matches pattern
• Matcher's find() method


  • Scans the input sequence looking for the next subsequence that matches the pattern
• String.split(regex)


  • Splits the string around matches of the given regular expression
• String.replaceAll(regex, replacement)


  • Replaces all the occurrences of the defined regular expression found in the string with another string