HSTP3301                                Code Refactoring                                  Johnson GoveasCopyright © Harbin...
Refactoring         – Refactoring refers to structuring the code to:              1.   Increase readability of code       ...
Why to refactor?         – Programs that are hard to read are hard to modify.         – Programs that have duplicated logi...
Why to refactor? Contd...         – To explain intention and implementation separately. Choosing           the name of eac...
When to refactor?         – Here’s a guideline from Don Roberts: The first time you do           something, you just do it...
Problems with refactoring         – Be careful while refactoring interfaces. An application using           this interface...
When not to refactor         – There are times when the existing code is such a mess that           although you could ref...
How to maintain code in a class   Use proper sections in your classes.      – View lifecycle: Generated default while addi...
Click to edit Master title style      WHAT TO REFACTOR?Copyright © Harbinger Systems   www.harbinger-systems.com   Code Ra...
Duplicate Code         If you see the same code structure (piece of code) in more than         one place, you can be sure ...
Long Methods         – Programs that live best and longest are those with short           methods.         – Longer a proc...
Large Class         – When a class is trying to do too much, it often shows up as too           many instance variables. Y...
Long Parameter List         – If you don’t have something you need, you can always ask           another object to get it ...
Divergent Change         – Divergent change occurs when one class is commonly changed           in different ways for diff...
Shotgun Surgery         – Shotgun surgery is similar to divergent change but is the           opposite. When similar chang...
Feature Envy         – If a feature / method of a class uses most of the data from           another class for its computa...
Data Clumps         – Often you might see few data items together in many places:           instance variables in a couple...
Primitive Obsession         – Do not be hesitant to use wrapper Objects over primitive data           types.         – Do ...
Case Statements         – Most times when you see a case statement you should           consider polymorphism.         – O...
Parallel Inheritance Hierarchies         – This is a special case of shotgun surgery.         – In this case, every time y...
Lazy Class         – A class that isn’t doing enough to pay for itself should be           eliminated.         – Often thi...
Speculative Generality         – You get it when people say, “Oh, I think we need the ability to           do this kind of...
Temporary Field         – Sometimes an instance variable is set only in certain           circumstances. Such code is diff...
Message Chains         – This occurs when a client asks one object for another object,           which the client then ask...
Middle Man         – If a class’s methods are delegating to this other classes for           data or logic, after a while ...
Inappropriate Intimacy         – Sometimes classes become far too intimate and spend too           much time into each-oth...
Alternative Classes with Different Interfaces         – Use Rename Method on any methods that do the same thing           ...
Incomplete Library Class         – This technique is used to enhance an existing third party           library.         – ...
Data Class (Model Classes)         – Such classes are dumb data holders and are almost certainly           being manipulat...
Refused Bequest         – Subclasses get to inherit the methods and data of their           parents. But what if they don’...
Comments         – If you need a comment to explain what a block of code does,           try Extract Method.         – If ...
Disjointed API         – A Library often presents itself as a relatively fine-grained,           disjointed API, with many...
After Effects         – Increase in reusability across projects – 70 to 80 %         – Ease in bug fixing – around 60 %   ...
References   1. Application Software Reengineering - By: M. Afshar      Alam and Tendai Padenga   2. Objective-C for Absol...
Click to edit Master title style                                   Thank You!Copyright © Harbinger Systems   www.harbinger...
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Code Refactoring

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What is Code Refactoring?

Refactoring refers to structuring the code to:
- Increase readability of code
- Fix bugs easily
- Enhance design
- Introduce flexibility to code.

Refactoring is to restructure or rewrite source code to improve internal consistency, readability, etc. without changing its function.

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  • Very interresting presentation. Usefull and clean to understand. I would also refer this *Refactoring* process as being named by others: Dogfooding.

    Daniel.
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Code Refactoring

  1. 1. HSTP3301 Code Refactoring Johnson GoveasCopyright © Harbinger Systems www.harbinger-systems.com Code Rafactoring
  2. 2. Refactoring – Refactoring refers to structuring the code to: 1. Increase readability of code 2. Fix bugs easily 3. Enhance design 4. Introduce flexibility to code. – Refactoring is to restructure or rewrite source code to improve internal consistency, readability, etc, without changing its function.Copyright © Harbinger Systems www.harbinger-systems.com Code Rafactoring
  3. 3. Why to refactor? – Programs that are hard to read are hard to modify. – Programs that have duplicated logic are hard to modify. – Programs that require additional behavior that requires you to change running code are hard to modify. – Programs with complex conditional logic are hard to modify. – To enable sharing of logic. For example, a sub-method invoked in two different places or a method in a super-class shared by all subclassesCopyright © Harbinger Systems www.harbinger-systems.com Code Rafactoring
  4. 4. Why to refactor? Contd... – To explain intention and implementation separately. Choosing the name of each class and the name of each method gives you an opportunity to explain what you intend. – To isolate change. Suppose, I use an object in two different places. I want to change the behavior in one of the two cases. If I change the object, I risk changing both. So I first make a subclass and refer to it in the case that is changing. – To encode conditional logic. Objects have a fabulous mechanism, polymorphic messages, to flexibly but clearly express conditional logic. By changing explicit conditionals to messages, you can often reduce duplication, add clarity, and increase flexibility all at the same time.Copyright © Harbinger Systems www.harbinger-systems.com Code Rafactoring
  5. 5. When to refactor? – Here’s a guideline from Don Roberts: The first time you do something, you just do it. The second time you do something similar, you wince at the duplication, but you do the duplicate thing anyway. The third time you do something similar, you refactor. – Refactor during design and analysis (UML diagrams) – Refactor when you add a function / feature – Refactor when you fix a bug – Refactor while code reviewCopyright © Harbinger Systems www.harbinger-systems.com Code Rafactoring
  6. 6. Problems with refactoring – Be careful while refactoring interfaces. An application using this interface from your library might stop working properly. (For example: support of deprecated methods) – With refactoring you approach the risks of change. Avoid refactoring of code that effects the application. – Think about enhancing and adding flexibility to design of the application while refactoring. – Even if you know exactly what is going on in your system, measure performance; don’t speculate.Copyright © Harbinger Systems www.harbinger-systems.com Code Rafactoring
  7. 7. When not to refactor – There are times when the existing code is such a mess that although you could refactor it, it would be easier to start from the beginning. – Avoid refactoring when you are close to release deadline. At that point the productivity gain from refactoring would appear after the deadline and thus be too late.Copyright © Harbinger Systems www.harbinger-systems.com Code Rafactoring
  8. 8. How to maintain code in a class Use proper sections in your classes. – View lifecycle: Generated default while adding a controller. – Event handling: Usually for controllers. This section will consist of methods like click to a button , change in selection, gesture recognition, etc. – Overloading methods: Methods overloaded from the super class – Delegates / Overriding: Separate section for methods of each protocol/delegate implemented. – Fetching data: This section will consists of refreshing UI and reloading of data. – Animation: This section will have all animation specific methods. NOTE: consider refactoring of these methods to generalize it.Copyright © Harbinger Systems www.harbinger-systems.com Code Rafactoring
  9. 9. Click to edit Master title style WHAT TO REFACTOR?Copyright © Harbinger Systems www.harbinger-systems.com Code Rafactoring
  10. 10. Duplicate Code If you see the same code structure (piece of code) in more than one place, you can be sure that your program will be better if you find a way to unify them: – Same code in two methods of the same class - Create a class method – Same code in two sibling subclasses - Create method in super class – Same code in two unrelated classes - Consider using Extract Class or Extract Module in one class and then use the new component in the other. Another possibility is that the method really belongs only in one of the classes and should be invoked by the other class or that the method belongs in a third class that should be referred to by both of the original classesCopyright © Harbinger Systems www.harbinger-systems.com Code Rafactoring
  11. 11. Long Methods – Programs that live best and longest are those with short methods. – Longer a procedure is, the more difficult it is to understand. – Whenever we feel the need to comment something, we should write a method instead. – The key here is not method length, but the semantic distance between what the method does and how it does it. – How do you identify the clumps of code to extract? A good technique is to look for comments. Conditionals and loops also give signs for extractions.Copyright © Harbinger Systems www.harbinger-systems.com Code Rafactoring
  12. 12. Large Class – When a class is trying to do too much, it often shows up as too many instance variables. You can Extract Class to bundle a number of related variables. – As with a class with too many instance variables, a class with too much code is prime breeding ground for duplicated code. If you have five hundred-line methods with a lot of duplicate code, you may be able to turn them into five ten-line methods with another ten two-line method extracted from the original.Copyright © Harbinger Systems www.harbinger-systems.com Code Rafactoring
  13. 13. Long Parameter List – If you don’t have something you need, you can always ask another object to get it for you. Thus with objects you don’t pass in everything the method needs; instead you pass enough so that the method can get to everything it needs. A lot of what a method needs is available on the method’s host class. – Example: To convert a date format, instead of creating a method in a utility class and passing parameter of the date and format required. We can create a category of date class with a method that takes the format required. Hence the class itself now has information for date, which was passed as parameter earlier.Copyright © Harbinger Systems www.harbinger-systems.com Code Rafactoring
  14. 14. Divergent Change – Divergent change occurs when one class is commonly changed in different ways for different reasons. If you look at a class and say, “Well, I will have to change these three methods every time I get a new database; I have to change these four methods every time there is a new financial instrument,” you likely have a situation in which two objects are better than one. That way each object is changed only as a result of one kind of change. – Identify everything that changes for a particular cause and use Extract Class to put them all together.Copyright © Harbinger Systems www.harbinger-systems.com Code Rafactoring
  15. 15. Shotgun Surgery – Shotgun surgery is similar to divergent change but is the opposite. When similar changes are all over the place, they are hard to find, and it’s easy to miss an important change. – In this case you want to use Move Method and Move Field to put all the changes into a single class. If no current class looks like a good candidate, create one.Copyright © Harbinger Systems www.harbinger-systems.com Code Rafactoring
  16. 16. Feature Envy – If a feature / method of a class uses most of the data from another class for its computation. – Consider shifting the method to that class instead.Copyright © Harbinger Systems www.harbinger-systems.com Code Rafactoring
  17. 17. Data Clumps – Often you might see few data items together in many places: instance variables in a couple of classes, and parameters in many method signatures. – The first step is to look for where the clumps appear as instance variables. Use Extract Class on the instance variables to turn the clumps into an object. – Then for parameters in method signatures, Introduce Parameter Object or Preserve Whole Object (refer Long Parameter List section above) to slim them down.Copyright © Harbinger Systems www.harbinger-systems.com Code Rafactoring
  18. 18. Primitive Obsession – Do not be hesitant to use wrapper Objects over primitive data types. – Do not be hesitant to create a class that may even have 2 or 3 primitive data types.Copyright © Harbinger Systems www.harbinger-systems.com Code Rafactoring
  19. 19. Case Statements – Most times when you see a case statement you should consider polymorphism. – Often the case statement matches on a type code. Consider using polymorphism in the class that hosts the type code value.Copyright © Harbinger Systems www.harbinger-systems.com Code Rafactoring
  20. 20. Parallel Inheritance Hierarchies – This is a special case of shotgun surgery. – In this case, every time you make a subclass of one class, you also have to make a subclass of another. – General strategy for eliminating this duplication is to make sure that instances of one hierarchy refer to instances of the other.Copyright © Harbinger Systems www.harbinger-systems.com Code Rafactoring
  21. 21. Lazy Class – A class that isn’t doing enough to pay for itself should be eliminated. – Often this might be a class that used to pay its way but has been downsized with refactoring. – Or it might be a class that was added because of changes that were planned but not made.Copyright © Harbinger Systems www.harbinger-systems.com Code Rafactoring
  22. 22. Speculative Generality – You get it when people say, “Oh, I think we need the ability to do this kind of thing someday” and thus want all sorts of hooks and special cases to handle things that aren’t required. – The result often is harder to understand and maintain. – If all this machinery were being used, it would be worth it. But if it isn’t, it isn’t. The machinery just gets in the way, so get rid of it.Copyright © Harbinger Systems www.harbinger-systems.com Code Rafactoring
  23. 23. Temporary Field – Sometimes an instance variable is set only in certain circumstances. Such code is difficult to understand, because you expect an object to need all of its variables. – Trying to understand why a variable is there when it doesn’t seem to be used can drive you nuts. – Use Extract Class to create a home for the poor orphan variables. Put all the code that concerns the variables into the component. You may also be able to eliminate conditional codeCopyright © Harbinger Systems www.harbinger-systems.com Code Rafactoring
  24. 24. Message Chains – This occurs when a client asks one object for another object, which the client then asks for yet another object, which the client then asks for yet another object, and so on. – Navigating this way means the client is coupled to the structure of the navigation. Any change to the intermediate relationships causes the client to have to change. – In principle you can apply Hide Delegate to potentially every object in the chain, but doing this often turns every intermediate object into a middle man (see the next point). Often a better alternative is to see what the resulting object is used for. See whether you can use Extract Method to take a piece of the code that uses it and then Move Method to push it down the chain. If several clients of one of the objects in the chain want to navigate the rest of the way, add a method to do that.Copyright © Harbinger Systems www.harbinger-systems.com Code Rafactoring
  25. 25. Middle Man – If a class’s methods are delegating to this other classes for data or logic, after a while it is time to use Remove Middle Man and talk to the object that really knows what’s going on. – Replace Delegation with Hierarchy to turn the real object into a module and include it in the middle man. That allows you to extend behavior without chasing all that delegation.Copyright © Harbinger Systems www.harbinger-systems.com Code Rafactoring
  26. 26. Inappropriate Intimacy – Sometimes classes become far too intimate and spend too much time into each-others (to and fro calls) classes for execution. – See whether you can arrange a Change Bidirectional Association to Unidirectional. If the classes do have common interests, use Extract Class to put the commonality in a safe place and make honest classes of them. Or use Hide Delegate to let another class act as go-between.Copyright © Harbinger Systems www.harbinger-systems.com Code Rafactoring
  27. 27. Alternative Classes with Different Interfaces – Use Rename Method on any methods that do the same thing but have different signatures for what they do. – Often this doesn’t go far enough. In these cases the classes aren’t yet doing enough. – Keep using Move Method to move behavior to the classes until the protocols are the same.Copyright © Harbinger Systems www.harbinger-systems.com Code Rafactoring
  28. 28. Incomplete Library Class – This technique is used to enhance an existing third party library. – Think of using categories / extensions for adding more functions to existing classes.Copyright © Harbinger Systems www.harbinger-systems.com Code Rafactoring
  29. 29. Data Class (Model Classes) – Such classes are dumb data holders and are almost certainly being manipulated in far too much detail by other classes. – Use Remove Setting Method on any instance variable that should not be changed. If you have collection instance variables, check to see whether they are properly encapsulated. – Look for where these getting and setting methods are used by other classes. Try to use Move Method to move behavior into the data class.Copyright © Harbinger Systems www.harbinger-systems.com Code Rafactoring
  30. 30. Refused Bequest – Subclasses get to inherit the methods and data of their parents. But what if they don’t want or need what they are given? – This means the hierarchy is wrong. You need to create a new sibling class and push all the unused methods to the sibling. – That way the parent holds only what is common.Copyright © Harbinger Systems www.harbinger-systems.com Code Rafactoring
  31. 31. Comments – If you need a comment to explain what a block of code does, try Extract Method. – If the method is already extracted but you still need a comment to explain what it does, use Rename Method. – If you need to state some rules about the required state of the system, use Introduce Assertion.Copyright © Harbinger Systems www.harbinger-systems.com Code Rafactoring
  32. 32. Disjointed API – A Library often presents itself as a relatively fine-grained, disjointed API, with many configuration options. – Often an individual project will not take advantage of all the configuration options. The same configuration options will be used over and over. – If this is the case, use a Gateway to interact with the API in a simplified way.Copyright © Harbinger Systems www.harbinger-systems.com Code Rafactoring
  33. 33. After Effects – Increase in reusability across projects – 70 to 80 % – Ease in bug fixing – around 60 % – Time saved while creating similar projects – around 50% – Increase in flexibility of design – around 70 %Copyright © Harbinger Systems www.harbinger-systems.com Code Rafactoring
  34. 34. References 1. Application Software Reengineering - By: M. Afshar Alam and Tendai Padenga 2. Objective-C for Absolute Beginners - By: Gary Bennett, Mitch Fisher and Bard Less 3. Refactoring: Ruby Edition - By: Jay Fields, Shane Harvie, Martin Fowler and Kent BeckCopyright © Harbinger Systems www.harbinger-systems.com Code Rafactoring
  35. 35. Click to edit Master title style Thank You!Copyright © Harbinger Systems www.harbinger-systems.com Code Rafactoring

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