Chapter 11: Anti-Patterns

Question 1

What is refactoring?

Answer 1

A refactoring is a correctness-preserving transformation that improves quality of the system

Question 2

Are anti-patterns refactored?

Answer 2

True, they are refactored to overcome their negative consquences.

Question 3

What are the state of affairs?

Answer 3

• One of six software projects are unsuccessful
• One third of software projects are cancelled
• Delivered system the budget and time to deliver is double as expected

Question 4

What is the God Class anti-pattern?

Answer 4

There is one god class that performs most of the work of the system while all other classes provide a very small role

Question 5

What is the problem with God Class?

Answer 5

Causes excessive message traffic

Question 6

Solution to the God Class?

Answer 6

Refactor the design to uniformly distribute intelligence to top-level classes in the system.

Locality principle.

Question 7

What is the Excessive Dynamic Allocation anti-pattern?

Answer 7

Excessive dynamic collection addresses frequent unnecessary creation and destruction of objects in the same class

Question 8

What is the problem with excessive dynamic allocation?

Answer 8

The time it takes to initialize the dynamic object on the heap and delete it off the heap ruins performance

Question 9

What is the solution to the excessive dynamic allocation?

Answer 9

Pre-allocate a “pool” of objects that are used frequently and store them in a collection or share objects.

Application of the processing vs frequency principle.

Question 10

What is the Circuitous Treasure Hunt?

Answer 10

Software retrieves data from a first table, uses those results to search a second table, retrieves data from the table and so on, until the “ultimate results” are obtained

Question 11

What is the problem with Circuitous Treasure Hunt?

Answer 11

Impact on performance is the large amount of data processing required to do the ultimate search.

Especially when figuring out the last call to make in the search.

Question 12

What is the solution to the Circuitous Treasure Hunt?

Answer 12

Select a different data organization if a database access problem occurs early in development

In distributed systems use adapter pattern to allow for a more reasonable interface for remote calls

Question 13

What is the adapter design pattern?

Answer 13

Adapters are used to enable objects with different interfaces to communicate with one another.

Question 14

What is the one-lane bridge anti-pattern?

Answer 14

One, or only very few processes are allowed to execute concurrently

Question 15

What is the problem with one-lane bridge anti-pattern?

Answer 15

All other processes must wait while other processes run.

Question 16

Solution to the one-lane bridge anti-pattern?

Answer 16

Allow for more resources to be shared for that more processes are allowed to run concurrently.

Follows the shared resource principle.

Question 17

What is the traffic jam principle?

Answer 17

The performance impact of the traffic jam is the transient behavior that produces wide variability in response time

Question 18

What is the problem with the traffic jam principle?

Answer 18

One-lane bridge produces many processes waiting for a turn which then means it takes time for the service to get back to normal

Question 19

What is the solution to the traffic jam principle?

Answer 19

If problem is caused by one-lane bridge then solving that pattern will help

If problem is caused by periodic high demand then use the spread-the-load principle.