What is the purpose of a delegation pattern?

Question

I was looking through the source to SensorManager in Android and found that when you register a SensorEventListener the SensorManager passes contro

Answer 1

As per effective Java (by Joshua Bloch), composition is favorable over inheritance. Composition has several advantages over inheritance. One of the intuitions for this is as follows: Consider a sub-class which inherits from a base class. So any change in the base class will make the sub-class fragile as the sub-class depends on the base class. By using inheritance, we are making a binding on the sub-class to depend on the base class, which makes our code fragile. However by using composition, we can remove this limitation. Composition is done by establishing a 'has-a relationship' between classes instead of 'is-a' relationship as in inheritance. 'Delegate pattern' and 'Decorator pattern' both are examples of how composition can be achieved. You might want to read the chapter on 'composition vs inheritance' in the effective java book as it is quite informative.

For shorter explanation, you can refer to this article: http://javarevisited.blogspot.com/2013/06/why-favor-composition-over-inheritance-java-oops-design.html