prefi

• Enumeration (enum)


  A data type that contains a fixed set of constants
• Enums


  • Good to use when you already know all possibilities of the values or instances of the class
  • Can be declared on their own or within another class
• To create an enum


  1. Declare a type with the enum keyword

  2. Declare an identifier for the type

  3. Declare a list of values called enum constants
• Enum methods


  • toString() - Returns the name of the calling constant object
  • ordinal() - Returns an integer that represents the constant's position in the list of constants; the first position is 0
  • equals() - Returns true if its argument is equal to the calling object's value
  • compareTo() - Returns a negative integer if the calling object's ordinal value is less than that of the argument, 0 if they are the same, and a positive integer if the calling object's ordinal value is greater than that of the argument
• Enum static methods


  • valueOf() - Accepts a string parameter and returns an enumeration constant
  • values() - Returns an array of the enumerated constants
• Type-safe


  Used to describe a data type that allows only appropriate behaviors
• Types of nested classes

  • Static member class - has access to all static methods of the top-level class
  • Non-static member class (inner class) - requires an instance; it has access to all data and methods of the top-level class
  • Local class - defined within a method body
  • Anonymous class - a special case of a local class that has no identifier
• The most common reason for nesting a class inside another is because the inner class is used only by the top-level class
• 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
• String.matches(String regex)


  Returns true if a string matches the given regular expression
• equals() method


  Compares one (1) string to another by comparing a single argument
• matches() method


  Allows you to determine what the string should match against and allows you to specify multiple values, providing much more flexibility in your code
• Pipe (|) symbol


  Allows the matches() method to check if a string is equal to "cat" or "dog" and return true accordingly
• Square brackets []


  Used in regular expressions to allow for character variability
• Square brackets are not restricted to two-character options, they can be combined with a hyphen to include any range of characters
• Dot (.)


  The 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
• The dot (.) represents any character, while the asterisk (*) represents any number of occurrences of the character preceding it. Hence, ".*" means any number of any characters in a sequence will return true
• Pattern class


  Stores the format of a regular expression
• Pattern.compile()


  Compiles the given regular expression into a pattern. A compiled regex pattern can speed up your program when the pattern is used frequently
• Matcher class


  Stores a possible match between a pattern and a string
• Matcher.matches()


  Checks if the regular expression given in the Pattern declaration matches a given string
• find()method

  Scans the input sequence looking for the next subsequence that matches the pattern
• split()method

  Splits the string around matches of the given regular expression
• replaceAll() method

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