inheritance vs delegation java

• inheritance vs  delegation java

Inheritance is used to create a hierarchical-type code structure that tries to keep as much “common” code near the top of the hierarchy.
In small, static systems, inheritance can be ok.
But large inheritance chains can also lead to hard-to-maintain code
design patterns that favor composition over inheritance for more info when to use inheritance and when not to.

Delegation is simply passing a duty off to someone/something else.
Delegation is alternative to inheritance.
Delegation means that you use an object of another class as an instance variable, and forward messages to the instance.


It is better than inheritance because it makes you to think about each message you forward, because the instance is of a known class, rather than a new class, and because it doesn’t force you to accept all the methods of the super class
you can provide only the methods that really make sense.
Delegation can also a powerful design/reuse technique.
The primary advantage of delegation is run-time flexibility
the delegate can easily be changed at run-time.


the choice between delegation and inheritance is driven by external factors such as programming language support for multiple inheritance or design constraints requiring polymorphism.

Consider threads in Java. You can associate a class with a thread in one of two ways: either by extending (inheriting) directly from class Thread, or by implementing the Runnable interface and then delegating to a Thread object

Often the approach taken is based on the restriction in Java that a class can only extend one class (i.e., Java does not support multiple inheritance). If the class you want to associate with a thread already extends some other class in the design, then you would have to use delegation; otherwise, extending class Thread would usually be the simpler approach

http://www.techartifact.com/blogs/2009/05/delegation-versus-inheritance-in-java.html#ixzz2CqNmtYMM