What is a key characteristic of composition in object-oriented design?

In object-oriented design, composition is a fundamental principle that allows developers to build complex classes using simpler, reusable components. This characteristic emphasizes creating new functionality by combining existing objects instead of inheriting behaviors from parent classes.

When a class is composed of other classes, it can leverage their functionalities while maintaining flexibility and encapsulation. This approach allows for better modularity; changes made to a composed class do not affect other classes directly. Additionally, composition supports code reuse, as developers can use existing components in multiple contexts without duplicating code.

While other characteristics such as defining class hierarchies and establishing relationships between classes are important in the broader scope of object-oriented design, they do not specifically capture the essence of composition. The focus on assembling behaviors via component objects sets composition apart as a key aspect of designing robust systems.