Bridge Design Pattern

What is Bridge design pattern?

The Bridge Design Pattern is used when there is one set of classes (abstraction) that define features and another set of classes (implementation) that provide the implementation for that features. You then ‘add’ a bridge by injecting the base of the implementation hierarchy to the base of the abstraction hierarchy. To get a more meaningful insight into the definition, imagine that you have an interface that defines some functionality. You will then implement that interface and create an implementation. Now consider that you want to add some more methods to the interface but you do not want all the classes to implement the new methods. What would you do? As a separate case, what if you want a class that just needs to implement one of the methods of the interface and ignore the others? Its cases such as these that are the ideal candidates for the bridge design pattern. The main actors of the pattern are

  • Abstraction

    -This class is the base of the abstraction hierarchy.

  • Refined Abstraction

    -These are the other classes of the abstraction hierarchy that extend the functionalities provided by the “Abstraction” class/interface.

  • Implementor

    -This is the base of the implementation hierarchy. The “Abstraction” class would hold a reference to this class/interface (hence the bridge). The methods for Implementor and Abstraction class could be different and the Implementor class generally holds methods that provide more fine grained functionalities.

  • Implementor

    -These are other classes of the implementation hierarchy

Bridge Design Pattern Example

To Demonstrate the bridge design pattern let us look at an example – Let’s say there is a Computer manufacturing company that wants to write a system for calculating the prices of their products. The prices depend on the base price and additional customs and excise, if any. The levy of the additional taxes depends on the country. We have two hierarchies here, the “abstraction” hierarchy includes the base pricing class and the derived customs and excise pricing classes. The “Implementation” hierarchy consists of a base implementation class and the country pricing classes extend this base class. Here’s the class diagram

Bridge Design Pattern Example

Bridge Design pattern reduces an explosion of classes by dividing the abstraction and implementation into two separate hierarchies.

There is no point using the bridge design pattern if there is only a single implementation class.

The exact implementation is determined at run time and different implementations can be plugged in at different times.

This finishes our tutorial on the bridge design pattern. remember bridge design pattern is the separation of implementation hierarchy from abstraction hierarchy.

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