Bridge

1
Bridge

• The decoupling of abstraction and implementation

2
Ideas

• GoF Intentions
• Decouple an abstraction from it implementation so
  that the two can vary independently
• Metsker
• Focuses on the implementation of an abstraction

3
Other Structural Patterns

• Adapter
• Composite
• Decorator
• Façade
• Flyweight
• Proxy

4
Uses

• You want to avoid a permanent binding between an
  abstraction and it's implementation. This might
  be the case, for example, when the implementation
  must be selected or switched at run-time.
• Both the abstractions and their implementations
  should be extensible by sub-classing. In this
  case, the Bridge pattern lets you combine the
  different abstractions and implementations and
  extend them independently.
• Changes in the implementation of an abstraction
  should have no impact on clients that is, their
  code should not have been recompiled.

5
Real Uses

• What are some common uses of the Bridge pattern?
• Drivers
• Applications
• System drivers
• Window Interfaces
• X Window System
• Microsoft Windows
• Application Programming Interfaces
• MFC
• JDBC

6
UML Diagram
7
Drivers

• JDBC is an application programming interface for
  executing SQL statements
• The drivers for JDBC and the applications that
  use JDBC are completely independent of each other
• The same application can use an Oracle driver
  just as easily as a MySQL or Postgres driver

8
Challenge 6.1

• Fill in the missing type names and the missing
  message name following illustration
• Class.forName(driverName)
• Connection c DriverManager.getConnection(url,
  user, passwd)
• Statement s c.createStatement()
• ResultSet r s.executeQuery(select name, apogee
  from fireworks)
• while(r.next())
• String name r.getString(name)
• int apogee r.getInt(apogee)
• System.out.println(name , apogee)

9
Challenge 6.1 Continued

• Fill in the missing type names and the missing
  message name following illustration

10
Abstract Class Refactoring

• Sometimes it is advantageous to refactor an
  abstract class to a Bridge pattern to gain more
  flexibility in the abstraction
• For instance, to separate the real-world
  implementation and a tester implementation

11
MachineController Refactoring

• Subclasses of MachineController exist for various
  types of machines and for various types of
  controllers
• Steps to refactor
• Move the abstract operations in the superclass
  into an interface
• Define implementation classes that provide
  different implementations of the interface
• Redefine the remaining operations in the abstract
  class as operations of the new interface

12
Challenge 6.3

• Fill in the missing labels for MachineController
  interface

13
Summary

• Decoupling interface and implementation
• Improved extensibility
• Hiding implementation details from clients
• Other Patterns and Bridge
• Abstract Factor can create and configure a
  particular Bridge
• The Adapter and Bridge patterns are similar, but
  usually the Adapter pattern is used after the
  classes are created where as the Bridge pattern
  is used from in the ground-up design