Consider composition instead of subclassing

Consider composition as an alternative to subclassing.

Composition:

Subclassing has the following issues: In addition:

A common exception is the template method design pattern. There, the safest style is to make all items in the abstract base class final, except for the single abstract method which needs to be implemented by the subclass.

An interesting quote from chapter one of Design Patterns:

"That leads us to our second principle of object-oriented design:

Favor object composition over class inheritance.

...Nevertheless, our experience is that designers overuse inheritance as a reuse technique, and designs are often made more reusable (and simpler) by depending more on object composition. You'll see object composition applied again and again in the design patterns."

(Their first principle, stated earlier in the chapter, is "Program to an interface, not an implementation".)

See Also :
Implementing compareTo
Implementing equals
Minimize ripple effects
Template method
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