[SOLVED] CS Java chain SE 333/433 Software

SE 333/433 Software
Testing & Quality Assurance Code-smells and bad-design practices
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Last Week
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Functional vs Non-Functional Requirements
Functional Requirements
Non-Functional Requirements
Execution Time
Size
Battery
Functionality of the program
Memory
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Text chat
Friends list
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Text chat Voice
Friends list Communication
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Text chat Voice
Friends list Communication
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Text chat Voice
Friends list Communication
-Execution time
-Battery consumption
-Size
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Text chat Voice
Friends list Communication
-Execution time
-Battery consumption
-Memory leak
-Size
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Functional Requirements
humans have to define these
Non-Functional Requirements
a machine can optimize these
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Functional Requirements
humans have to define these
Non-Functional Requirements
a machine can optimize these
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Software Refactoring:
Antipatterns Detection
Antipatterns Correction (Refactoring Recommendation)
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Another System Model (Data- Bases)
Model transformation
System Model (in UML)
Program (in Java)
Forward engineering
Model space
Source code space
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Reverse
engineering m
Refactoring
Anothe r Progra
(Java)

Refactoring
The process of improving a code after it has been written by changing its internal structure without changing the external behavior (Fowler et al., 99)
Examples: Move method, extract class, move attribute,
Two main refactoring steps
1.detection of code fragments to improve (e.g., Anti pattern) 2.identification of refactoring solutions
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Learning objectives
Anti-patterns: Overview
Examples of anti-patterns
How to detect anti-patterns using quality metrics?

Design defects/antipatterns
Design defects/antipatterns are poor coding and design choices introduced during different phases of software development
Anomalies, code smells , bad smells
Make the design harder to understand, to change
Design situations that adversely affect the development of a software (not bugs)
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Management Antipatterns
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Examples of antipatterns
Duplicated code
Long method
God class
Long parameter list Message chain
Data class
Functional decomposition
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Definition
The Blob (God Class)
Procedural-style design leads to one object with numerous responsibilities and most other objects only holding data or executing simple processes.
Symptoms
A Blob is a controller class, abnormally large, with almost no parents and no children. It mainly uses data classes, i.e. very small classes with almost no parents and no children (Brown et al. 98).
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Causes
Lack of an object-oriented architecture.
Inadequate understanding of OO principles Lack of (any) architecture
Design, interaction between object etc. Too limited intervention
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Duplicate Code or
Cut and Paste Programming
Code reused by copying source statements leads to significant maintenance problems.
Duplicate methods in subclasses
Duplicate expressions in same class
Duplicate expressions in different classes
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Large method
A method that does more than one thing Many things, sometimes unconnected things
Problems
Could indicates low levels of abstraction, low level of class design,
reduced re-usability
Harder to test, poor readability
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Long Parameter List
Introduce parameter object
Only worthwhile if there are several methods with same
parameter list, and they call each other
user= userManager.create(USER_NAME,group, USER_NAME, test, Language, false, false, new Date(), blah, new Date())
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Message Chain
Long list of method calls:
customer.getAddress().getState()
window.getBoundingbox().getOrigin().getX()
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Message Chain
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Data Class/Lazy Class
Class has no methods except for getter and setters
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Switch statements
Switch statements are very rare in properly designed object- oriented code
Therefore, a switch statement is a simple and easily detected bad smell
Of course, not all uses of switch are bad
A switch statement should not be used to distinguish between various kinds of object
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Example 1, continued
class Animal {
final int MAMMAL = 0, BIRD = 1, REPTILE = 2; int myKind; // set in constructor

String getSkin() {
switch (myKind) {
case MAMMAL: return hair; case BIRD: return feathers; case REPTILE: return scales; default: return skin;
} }
}

Example 1, improved
class Animal {
String getSkin() { return skin; } }
class Mammal extends Animal {
String getSkin() { return hair; } }
class Bird extends Animal {
String getSkin() { return feathers; } }
class Reptile extends Animal {
String getSkin() { return scales; } }

Dead Code/ Old Baggage
Description
System contains many classes whose purpose is not known
Lava Flow, Dead Code
Much of the code is left over from previous ideas and no longer has a purpose
was once fluid and useful, now is solid lava that you are afraid to remove
Consequences
difficult to maintain, just gets worse
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Comments?
The purpose of comments should be only why you are doing something (to help future modifiers_ rather than what code is doing
Whenever possible make your code express the intent of the comment and remove the comment.
Comments are to provide intent that is not expressible in code
Any comment that duplicates what the code says should be deleted
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Shotgun Surgery
This happens when, you want to make some kind of change, your are forced to make a lot of changes to a lot of different classes
And when changes are all over the place, they are hard to find, and its easy to miss an important change
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Functional Decomposition
Description
Classes with names functions
All class attributes are private and are used only inside the class Classes with a single action similar to a procedural function.
Consequences
No O/O benefits such as inheritance and polymorphism Expensive to maintain
Complexity of testing software Complexity of reuse of the code
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Spaghetti code
Description
System hard to debug, modify
Bunch of code similar in structure to a bowl of spaghetti.
Bad coding practices
Consequences
Low readability
Impossible to understand how it exactly works
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Feature envy
When a method seems more interesting in a class, other than the one in actually it is
Example : a method that invokes half a dozen getting methods on another object to calculate some value.
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Class Activity
See additional file added on d2l
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