Building complex objects by combining simpler ones is known as what?

The concept of building complex objects by combining simpler ones is referred to as composition. In object-oriented programming, composition allows for the creation of complex data types by combining objects that represent simpler, more fundamental concepts. This method promotes a modular approach to software design, where different objects can be combined in various ways to create new functionality without altering the constituent objects themselves.

In composition, an object is made up of one or more other objects, thus forming a "has-a" relationship, which enables modeling of real-world relationships more intuitively. For example, a car object can be composed of several simpler objects, such as an engine, wheels, and chassis, each of which can be defined as separate classes. This way, if there are changes in one part, it does not necessarily impact the others, reflecting better maintainability and reusability.

Other concepts like inheritance, aggregation, and polymorphism serve different purposes. Inheritance allows a class to inherit attributes and methods from another class, establishing an "is-a" relationship. Aggregation involves a relationship where a class is made up of other classes but where the contained classes can exist independently. Polymorphism allows methods to be defined in different ways depending on the object, providing flexibility in method invocation.