A cohesive class gives its members one clear primary responsibility. Its purpose is easy to understand and its code is easier to maintain because related state and behavior change together. section 2.3.1
Separate automobile responsibilities
An AutomobileApp that operates, maintains, and cleans a car is not cohesive. Refactor it into Automobile for operation, Garage for maintenance, and CarWash for cleaning. Each class then has one primary reason to change. section 4.2.1
Listing 4.1 (Program 4.1 Automobile-1): AutomobileApp.h (not cohesive)
class AutomobileApp
{
public:
void accelerate(); #1
void adjust_headlights(); #1
void apply_brakes(); #1
void change_oil(); #1
void change_tires(); #1
void check_brakes(); #1
void check_tires(); #1
void rotate_tires(); #1
void shut_off_engine(); #1
void start_engine(); #1
void tuneup_engine(); #1
void turn_left(); #1
void turn_right(); #1
void vacuum_car(); #1
void wash_car(); #1
void wax_car(); #1
private:
Brake brakes[4]; #2
Engine engine; #2
Oil engine_oil; #2
Direction heading; #2
Headlight headlights[4]; #2
int speed; #2
Soap soap; #2
Tire tires[4]; #2
Vacuum vacuum_cleaner; #2
CarWax wax; #2
};
Inspect the mixed-responsibility AutomobileApp interface before comparing it with the cohesive Automobile and Garage design. section 4.2.1
