I had this question on my test:
What kind of programming / design pattern is this:
FileReader fr = new FileReader("file.txt"); BufferedReader bf = new BufferedReader(fr);
I'm sorry for the trouble, but definitions of programming patterns are unclear for me and I don't know how to answer this question correctly.
That's an example of the Decorator Pattern.
As the linked Wikipedia article states:
Decorator pattern is a design pattern that allows behaviour to be added to an existing object dynamically.
In your example, you're adding buffering to a FileReader, which provides more efficient reading than a regular, un-buffered FileReader.
This is Decorator pattern. From Design Patterns book:
Intent: attach additional responsibilities to an object dynamically. Decorators provide a flexible alternative to subclassing for extending functionality
...
Applicability: Use Decorator
- to add responsibilities to individual objects dynamically and transparently, that is, without affecting other objects.
- for responsibilities that can be withdrawn.
- when extension by subclassing is impractical. Sometimes a large number of independent extensions are possible and would produce an explosion of subclasses to support every combination. Or a class definition may be hidden or otherwise unavailable for subclassing.
In case of BufferedReader, it attaches buffering feature to FileReader.
If you want to know more about patterns, I recommend reading this book (or more lighter "Head First Patterns"). Additionally, there's brilliant answer on SO about patterns usage inside JDK -- very cool stuff!
