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Definition:
The intent of Observer pattern is to define a one-to-many dependency between objects so that one object changes state, all its dependents are notified so that they can react to the change.
What is:
Observer pattern
Example:
1. Bob Tarr’s observer pattern
2. Enhance design patterns with AspectJ, Part 2
3. Observer and Observable-An introduction to the Observer interface and Observable class using the Model/View/Controller architecture as a guide
4. The Observer Pattern Revisited
Summary:
For small application, a common practices is to register a single object to receive all events in a GUI. There is no inherent problem with this, but you should recognize that it reverses the distribution of responsibility that OBSERVER intends.
For a large GUI, consider moving to an MVC design, letting each interested object register for events rather than introducing a mediating central object. MVC also lets you create loosely coupled layers that can change independently and that may execute on different machines.
Most of computer science students won’t forget the pain of learning data structure and algorithm. If you work at Google or NASA, then you may use it everyday. Why data structure and algorithm is so important and how to refactor your code? think about this,
For example, write a function to display all Fibonacci numbers for given number.
function fib1(n)
if n = 0: return 0
if n = 1: return 1
return fib1(n – 1) + fib1(n – 2)
If you write code like above, then the bigO would grow up to 2^n. In short, our naive recursive algorithm is correct but hopelessly ineffcient. Can we do better?
function fib2(n)
if n = 0 return 0
create an array f[0 : : : n]
f[0] = 0, f[1] = 1
for i = 2 : : : n:
f[i] = f[i - 1] + f[i - 2]
return f[n]
The bigO would be linear in n.
Do you see the big different? remeber whenever we have an algorithm, there are three questions we always ask about it:
1. Is it correct?
2. How much time does it take, as a function of n?
3. And can we do better?
Ref:
Algorithms from S. Dasgupta, C.H. Papadimitriou, and U.V. Vazirani
Data Structures and Algorithms
Wiki: Algprithm
