What composition over inheritance is
Composition over inheritance is a design principle that favors building an object's behavior by combining other objects, rather than by inheriting from a base class. Both composition and inheritance are ways to reuse and structure behavior, but this principle suggests that composition is often the better default. It encourages assembling functionality from parts instead of relying on class hierarchies.
Composition and inheritance
Inheritance builds a new class based on an existing one, taking on its behavior. Composition, by contrast, builds behavior by including other objects as parts and delegating to them. Both let you reuse behavior, but they do so differently. Inheritance creates a strong is-a relationship, while composition creates a has-a relationship, combining capabilities from included pieces.
Why composition is often preferred
Composition is often preferred because it tends to be more flexible. With composition, behavior can be assembled and changed by combining different parts, without being locked into a fixed class hierarchy. Inheritance can create rigid structures where changes to a base class ripple through everything that inherits from it. Composition avoids some of this rigidity, making designs easier to adjust.
Flexibility and change
A major advantage of favoring composition is adaptability. Because behavior is built from interchangeable parts, it can be reconfigured as needs change. This makes it easier to vary and extend functionality. Inheritance, while useful, can make such changes harder when hierarchies grow deep or when behavior does not fit neatly into an is-a relationship. Composition offers a more modular alternative.
Using the principle wisely
Composition over inheritance is a guideline, not an absolute rule; inheritance still has its place where it genuinely fits. The principle simply advises reaching for composition first, especially when flexibility matters. Understanding this principle clarifies a common piece of design wisdom: prefer building behavior by combining parts over relying heavily on class inheritance.
Why it matters
Composition over inheritance is an important principle in software design. Understanding what it is - favoring combining objects over inheriting from a base class - clarifies how to build flexible, adaptable software. For anyone learning object-oriented design, it is a valuable concept to understand.
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See also: What is object-oriented programming? Explained, What is inheritance in programming?.
Sources
Published date reflects the original event date (2026-10-18). This article is original Skillo editorial written from the sources above; facts were verified in September 2026.
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