As the third topic in my article series Introduction to Object-Oriented Programming in LabVIEW I’ll talk about inheritance and conceptual hierarchies in object oriented programming.

Hierarchies of real-world objects

Object of the real world often form conceptual hierarchies. For example a bicycle, a motorcycle and a car are all examples of different kinds of vehicles. A bus, a truck and an SUV are examples of different kinds of cars. These relationships between similar objects can be visualized using diagrams similar to one below.

All vehicles share common properties and common functionality. For example all vehicles have one or more wheels and they are designed for transportation purposes. We can also fairly safely say that all vehicles have some sort of steering method.

All cars share even more common properties and common functionality. A steering wheel is used for steering the cars. An engine is used as a power source. All cars have at least four wheels and the wheels are symmetrically distributed on both sides of the car.

We can say that the word vehicle defines a class of real-world objects for transportation and so does the words car, bicycle and motorcycle. As cars, bicycles and motorcycles are all special kinds of vehicles as well we can say that words car, bicycle and motorcycle all define subclasses of class vehicle. In a similar way bus, truck and SUV can all be considered subclasses of class car as they are special kinds of cars.

Class hierarchies in object-oriented programming

It’s often the case that the building blocks of a software project form similar conceptual relationship hierarchies. Consider for example the following build-in LabVIEW types.

All of these build-in types are numeric types. Furthermore EXT, DBL, SGL, CXT, CDB and CSG are floating point numbers whereas I64, I32, I16, I8, U64, U32, U16 and U8 are integer numbers. We can divide integers to signed and unsigned integers and floating point numbers to real and complex numers. Indeed these numeric types can be considered to form a conceptual hierarchy similar to one below.

Object-oriented programming allows the developer to specify this kind of conceptual hierarchies in software architecture. Each box in the above image can be considered to be a class. Remember from my last article that classes are building blocks in object-oriented programming that encapsulate both data and functionality.

This concept of hierarchies is called inheritance in object-oriented programming. The word inheritance comes from the fact that the classes in the hierarchy inherit properties, functionality and interfaces of their parents and all other ancestors. The diagram itself is called a class diagram as it represents the relations between different classes.

Conclusions

In object-oriented programming developers can define class hierarchies that define the relations of classes. Decedent classes inherit the functionality, the interface and the data type of all the ancestor classes. Although it didn’t yet become clear, class hierarchies and inheritance is one of the key substances in object-oriented programming. Class hierarchies greatly enhance code reuse and allow creating more intuitive software architectures.

In my next article I’ll go into more detail what are the benefits of inheritance. Subscribe to the RSS feed so you will not miss it.