Implementing a Time Abstract Data Type with a class

• Classes
  • Model objects
    • Attributes (data members)
    • Behaviors (member functions)
  • Defined using keyword class
  • Member functions
    • Methods
    • Invoked in response to messages
• Member access specifiers
  • public: Accessible wherever object of class in scope
  • private: Accessible only to member functions of class
  • protected:
• Constructor function
  • Special member function
    • Initializes data members
    • Same name as class
  • Called when object instantiated
  • Several constructors; Function overloading
  • No return type

  1  class Time {
  2
  3  public:
  4     Time();                        // constructor
  5     void setTime( int, int, int ); // set hour, minute, second
  6     void printUniversal();         // print universal-time format
  7     void printStandard();          // print standard-time format
  8
  9  private:
  10   int hour;     // 0 - 23 (24-hour clock format)
  11   int minute;   // 0 - 59
  12   int second;   // 0 - 59
  13
  14  }; // end class Time
  

• Objects of class
  • After class definition
    • Class name new type specifier; C++ extensible language
    • Object, array, pointer and reference declarations
  • Example:

    Time sunset;
    Time arrayofTimes[ 5 ]; 
    Time *pointerToTime;
    Time \&dinnerTime = sunset;
    

• Member functions defined outside class
  • Binary scope resolution operator (::)
    • Ties member name to class name
    • Uniquely identify functions of particular class
    • Different classes can have member functions with same name
  • Format for defining member functions

    ReturnType ClassName::MemberFunctionName( ){ 
    .
    .
    .
    }
    

  • Does not change whether function public or private
• Member functions defined inside class
  • Do not need scope resolution operator, class name
  • Compiler attempts inline; Outside class, inline explicitly with keyword inline

  Figure 4: Time abstract data type implementation as a class, (part 1 of 3).

  

  

  Figure 5: Time abstract data type implementation as a class, (part 2 of 3).

  

  

  Figure 6: Time abstract data type implementation as a class, (part 3 of 3).

  
• Destructors
  • Same name as class; Preceded with tilde (~)
  • No arguments
  • Cannot be overloaded
  • Performs termination housekeeping
• Advantages of using classes
  • Simplify programming
  • Interfaces; Hide implementation
  • Software reuse
    • Composition (aggregation); Class objects included as members of other classes
    • Inheritance; New classes derived from old