09 Software Refactoring

Question 1

what are code smells

Answer 1

1. poor structure

2. inappropriate coupling between modules

Question 2

what is refactoring

Answer 2

1. change made to internal structure
2. make it easier to understand, cheaper
3. behaviour remains the same

Question 3

refactoring flow

Answer 3

1. identify refactor opportunity
2. create test cases
3. plan refactoring
4. apply refactoring
5. run tests
6. commit

Question 4

when to refactor

Answer 4

1. implementing new functions
2. correcting defects
3. code reviews
4. detecting code smells
5. trying to understand how artefact works

Question 5

types of code smells

Answer 5

1. cloning
2. complex structures
3. variables and parameters
4. making changes
5. control structures
6. design uncertainty
7. delegation

Question 6

1. cloning

Answer 6

1. duplicated code
   - cloned rather than reused
   - use extract method

Question 7

2. complex structures

Answer 7

1. long method
   - contain too many lines of code
   - use extract method
2. large class
   - contain too many methods, fields
   - too much responsibilities
   - use extract class

Question 8

3. variables and parameters

Answer 8

1. long parameter list
   - too many parameters for a method
   - replace parameters with method
2. feature envy
   - method use data of another class extensively more than its own data
   - use move method (move method to another class)
3. data clumps
   - different parts of code contain identical group of variables
   - use extract class to form new class
4. primitive obsession
   - rely too much on primitive data types
   - create object for data types
5. temporary fields
   - variables in method not always needed
   - use extract class

Question 9

4. making change

Answer 9

1. divergent change
   - when single class is changed, forced to change many other dependent unrelated method
   - use extract class to split
2. shotgun surgery
   - making change requires making many small changes to different class
   - use move method to a single class
3. parallel inheritance
   - creating a subclass to create subclasses
   - use move method to remove hierarchy
4. switch statement
   - too many if statements
   - use extract method
5. refused bequest
   - subclass do not need super class methods
   - push down methods to subclass and remove hierarchy
6. alternative classes with interface
   - 2 classes perform identical function but with different name
   - use rename method

Question 10

5. design uncertainty

Answer 10

1. lazy class
   - insufficient independent responsibilities
   - use inline class
2. speculate generality
   - unused methods, class, parameters
   - for future uses
   - comment out
3. incomplete library class
   - libraries stop meeting user requirements but cannot be deleted
   - introduce foreign method

Question 11

6. delegation

Answer 11

1. message chain
   - one object access data item through a series of calls
   - use hide delegation, extract and move method
2. middle man
   - object act as information broker to another object but does not provide any other responsibilities
   - use remove middleman, inline method
3. data class
   - class has no method other than getters and setters
   - lacks behavioural responsibilities
   - use extract method, move method

Question 12

what is self documenting code

Answer 12

excessive use of comments to explain unnecessary complex structures

reduce the need for supplementary documentation

Question 13

extract method

Answer 13

pros

• more readable code
• less duplication

Question 14

inline method

Answer 14

pros

- minimise number of unneeded methods

Question 15

move method

Answer 15

pros

- reduce dependency between class

Question 16

extract class(split)

Answer 16

pros
 - single responsibility class are more reliable, tolerant to changes

Question 17

inline class

Answer 17

pros

- eliminate needless class

Question 18

encapsulate fields

Answer 18

PRIVATE String name

pros
- bring data closer together

Question 19

replace data with class

Answer 19

pros

- group primitive data types into its own class

Question 20

replace magic number with symbolic constant

Answer 20

pros

- reduce duplicate use of number or string

Question 21

replace method with class

Answer 21

pros
- isolate long method

cons
 - another class is added which increases complexity

Question 22

parameterise method

Answer 22

pros

- combine multiple methods by using parameters

Question 23

remove parameters

Answer 23

pros

- method only contain parameters it truly requires

Question 24

introduce parameter objects

Answer 24

pros

- replace repeating group of parameter with class

Question 25

decompose conditional

Answer 25

pros

- decompose conditional codes to clearly named methods

Question 26

consolidating conditional expressions

Answer 26

pros

- eliminate duplicate control flow codes

Question 27

replace conditionals with polymorphism

Answer 27

pros

- remove duplicate and almost identical conditions