7.1. Objects in High Level Languages

When we declare a class in a high level programming language, we define a collection of data and some ways to manipulate that data. We write something like the Time class below to indicate that a Time consists of there integers and that we can do things with a Time object like change the minute value and retrieve the hour value.

class Time {
private:
   int second;
   int minute;
   int hour;

public:
   Time();
   Time(int h, int m, int s);
   int getMinute();
   void setMinute(int m);
   void incrHour();
   int getHour();
};

Every Time has its own data (hours, minutes, seconds), but they all share the same functions. There is only one Time::getMinute() function. The same code will execute no matter which Time object we call getMinute on. However, the data that code operates on will depend on what object is executing the code. In the sample below, we call getMinute() on time1, so as the Time::getMinute() will be operating on the data of time1.

Time time1(12, 45, 00);
Time time2(8, 30, 00);
int x = time1.getMinute();

To access the data of the object that the function was called on, the function accesses this meaning “the current object”. this is not passed explicitly as a parameter, it is implicit in the way the function was called.

int Time::getHour() {
   return this->hour;
}
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