Ooad 2 Interfaces And The Facade Pattern
- 1. OOAD 2 Interfaces and the Facade pattern
- 2. A bit about interfaces “ Always Program to an Interface” We don’t necessarily mean a Java-style Interface language construct I guess you could simplify it to: Always program to a supertype
- 3. “ Always Program to an Interface” To an implementation: Dog d = new Dog(); d.bark(); To an interface: Animal a = getAnimal(“dog”); a.makeSound();
- 4. Advantages? We’re not worrying about implementations Can deal with things generically (more abstraction), reducing code Greater resilience to change We’ll see more advantages as we cover more patterns in the coming weeks
- 5. Facade pattern Takes a complex subsystem and makes it a simpler one
- 6. Subsystem Class 1 Class 5 Class 4 Class 3 Class 6 Class 2
- 7. Subsystem Class 1 Class 5 Class 4 Class 3 Class 6 Class 2 Client class
- 8. Subsystem Class 1 Class 5 Class 4 Class 3 Class 6 Class 2 Facade Client class
- 9. Subsystem Class 1 Class 5 Class 4 Class 3 Class 6 Class 2 Facade Client class Client class 2
- 11. Facade pattern summary Takes a complex subsystem and makes it a simpler one You can still directly access the underlying classes Example: home theatre controller Simple, unified interface Most common functions in one place You can still use the individual controllers
- 12. When to use it? To provide an easy interface to lots of subsystems Principle of Least Knowledge – reduce interactions between objects Reduces the amount of “spaghetti”