Introduction to Design Patterns and Singleton

Design Patterns 05/27/10 Week 1 : Introduction and Singleton Jon Simon [email_address]

Agenda ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

What is a Design Pattern? ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],05/27/10

Why Study Design Patterns? ,[object Object],[object Object],[object Object],[object Object],05/27/10

History of Design Patterns ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],05/27/10

History (continued) ,[object Object],[object Object],[object Object],05/27/10

The Gang of Four ,[object Object],[object Object],[object Object],[object Object],[object Object],05/27/10

The Gang of Four: Pattern Catalog 05/27/10 Patterns in red will be discussed in class. ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

How Design Patterns Solve Design Problems ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],05/27/10

Reality ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],05/27/10

Tangent: Unit Testing ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],05/27/10

Unit Testing (cont) ,[object Object],[object Object],[object Object],[object Object],05/27/10

Unit Testing: Final Thoughts ,[object Object],[object Object],[object Object],[object Object],[object Object],05/27/10

Common Pitfall ,[object Object],[object Object],[object Object],05/27/10

The Book ,[object Object],[object Object],[object Object],[object Object],[object Object],05/27/10

Example: Logger ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Example: Logger (cont) ,[object Object],[object Object],[object Object]

Singleton ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],05/27/10

Logger – as a Singleton ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],05/27/10 Note the parameterless constructor See pg 173 in book

Lazy Instantiation ,[object Object],[object Object],[object Object],05/27/10

Singleton vs. Static Variables ,[object Object],[object Object],[object Object],[object Object],[object Object]

Threading ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],05/27/10 What would happen if two different threads accessed this line at the same time?

Option #1: Simple Locking ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Option #2 – Double-Checked Locking ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],pg 182

Option #2 (C# Example) ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],05/27/10

Option #3: “Eager” Initialization ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],05/27/10 ,[object Object],[object Object],Runtime guarantees that this is thread-safe pg 181

Lab #1: Turn a class into a Singleton ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],05/27/10 Take this class and turn it into a Singleton.

Lab #1 Answer ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Lab #2 ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],05/27/10

Lab #2 (cont) ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],05/27/10

Lab #2 (cont) ,[object Object],05/27/10

Lab #2 (cont) ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],05/27/10

Lab #2 (cont) ,[object Object],[object Object],[object Object],05/27/10

Lab #2 Answers ,[object Object],[object Object],[object Object],[object Object],[object Object]

Inheritance Summary ,[object Object],[object Object],[object Object],05/27/10

Add Registry to Singleton ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

SingletonRegistry Class ,[object Object],[object Object],[object Object],[object Object]

Case Study: Dependencies ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],05/27/10

Case Study: Dependencies ,[object Object],[object Object],[object Object]

Case Study: Dependencies ,[object Object],[object Object],[object Object],05/27/10

Unit Testing ,[object Object],[object Object],[object Object],[object Object],05/27/10

Unit Testing ,[object Object],[object Object],[object Object],05/27/10

Scott Densmore “Why Singletons are Evil” ,[object Object],[object Object],[object Object],[object Object],[object Object],05/27/10

Jeremy D. Miller “Chill out on the Singleton…” ,[object Object],[object Object],[object Object],05/27/10

“ How to Decontaminate a Singleton” ,[object Object],[object Object],05/27/10

Comments from Others ,[object Object],[object Object],[object Object],05/27/10

Other Useful Articles ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

SUMMARY ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],05/27/10

Introduction to Design Patterns and Singleton

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