designing good api & its importance
DESCRIPTION
This is a presentation inspired (heavily) by that of Joshu Bloch's presentation on "How to design a good API and its importance". I tried to simplify on API importance and tried to generify how to conceive it. No point referring to that presentation explicitly as I am mentioning it here and mentioned it at the start and end of the presentation as I made it in BASIS SoftExpo 2012TRANSCRIPT
- 1. Designing Good APIandits importance Imran M Yousuf Entrepreneur Smart IT Engineering Ltd.
2. Outline
- What is an API?
3. Why is API important? 4. Designing API 5. General Principles 6. OOP Design Principles Smart IT Engineering Ltd. 7. What is an API?
- APIstands for Application Programming Interface
8. API is a source code-basedspecification intended to be used as an interface bysoftware components to communicatewith each other. 9. ABI (Application Binary Interface) differs to API in that the former is specified on binary interface 10. In this presentation we will consider ABI as API too Smart IT Engineering Ltd. 11. Why is API important?
- What do we Software Engineers develop? How do others interact with our software?
12. Do we integrate Facebook API (FB Login, Like, Share, etc.)? How? 13. How do we develop softwares that require system level integration? 14. How do Web 2.0 portals communicate with its server? 15. How do Smart Phone / Tablet Apps communicate with server? Smart IT Engineering Ltd. 16. Why is API important?
- We, software engineers, develop softwares which users use through UI, write plugins for, use as a library and/or use by executing and working with the output of the software.
17. A lot of (Almost all) websites integrate with FB using its JavaScript API 18. For Windows we use MFC or Windows API; for *nix system we use POSIX etc. 19. Web 2.0 / Smart Phone / Tablet Apps make server side calls via HTTP protocol either from a App or from browser using AJAX. Smart IT Engineering Ltd. 20. Why is API important?
- All of this signifies -Software components communicate with each other So either we aredeveloping and using APIeveryday. That is not enough for getting our attention?
Smart IT Engineering Ltd. 21. Why is API important?
- Imagine the following
- FB JavaScript API is so difficult to use that you are not able to use them. What would you do?
22. You are developing an Android or iPhone App and having problem using their API as you not understanding how to simply achieve them. What would you do? 23. Your client asked you to use a Web Service to integrate one service to another and the Web Service makes no sense what so over and furthermore, it does not have ample documentation. What would you do? 24. What would be your opinion of such API providers? Smart IT Engineering Ltd. 25. Why is API important?
- Contact FB and ask them how to use it
26. Contact Andoid community mailing lists/forums and ask there 27. Contact iPhone Developer Community and ask there 28. Ask my customer to get me documentation or ask the company/developer for help 29. We think those companies and their developers are crap and we are better than them Smart IT Engineering Ltd. 30. Why is API important?
- API can cause a Company and its Developer both Glory and Gloom depending on its user experience
31. API can be among a company's greatest assets
- Customers invest heavily: buy, write, learn
32. Cost to stop/change API can be prohibitive 33. Successfully Public APIs capture customers Bad API causes unending support request and becoming a liability to the company Smart IT Engineering Ltd. 34. Why is API important?
- If you code, you are an API designer
- Good code is modular each module has an API
Useful modules tend to get reused
- Once module has users, can't change API at will
35. Good reusable modules are corporate assets Thinking in terms of APIs improves code quality Smart IT Engineering Ltd. 36. Characteristics of a Good API
- Easy to learn
37. Easy to use, even without documentation 38. Hard to misuse 39. Easy to read and maintain code that uses it 40. Sufficiently powerful to satisfy requirements 41. Easy to extend 42. Appropriate to audience Smart IT Engineering Ltd. 43. Designing API Smart IT Engineering Ltd. 44. Gather Requirements
- We usually get a project to work in the form of a solution
- We should keep in mind better solutions may exist
We must extract true requirements in form ofuse-cases . 45. Can be easier and more rewarding to build something more general
- Beware of the cost factor and target audience
Smart IT Engineering Ltd. 46. Start with short spec
- Start of all API should begin with writing a spec, preferably within 1 page
47. At the very beginning agility trumps completeness 48. Bounce spec off as many head as possible
- Listen to their input seriously
Once confidence is there that we understand what it is grow the spec
- This growing could involve coding, e.g., prototypes
Smart IT Engineering Ltd. 49. Write it early & often
- API comes before the implementation
- API is the concept and should elaborate on behavior
50. Thus saving implementing something that is not useful API code helps you show the spec itself
- Saves time in writing documents that is useless
Continue writing to API Smart IT Engineering Ltd. 51. Write an SPI
- Service Providers Interface (SPI)
- Plugin API enabling multiple implementations
52. It serves as an API used by API implementations 53. For example, Data Access Layer implementations Write multiple SPI implementations before release
- If its a target that we want to support multiple implementations then we should implement at least a couple of them.
54. If you write one, it probably won't support another 55. If you write two, it will support more with difficulty 56. If you write three, it will work fine Smart IT Engineering Ltd. 57. Maintain Realistic Expectation
- Most API designs are over constrained
- You won't be able to please everyone
58. Aim to displease everyone equally 59. Stick to what you want to achieve Expect to make mistakes
- Real world use will continuously flush out the mistakes
60. Expect to evolve API Smart IT Engineering Ltd. 61. General Principles Smart IT Engineering Ltd. 62. Should Do One Thing & Do It Well
- Functionality should be easy to explain
- If it's hard to name, it indicates rethink
63. Good names enables API to thrive 64. Be open to splitting and merging modules Functionality should be well specified
- Specify how the API should be used
65. Write tests demonstrating API usage 66. Specification will get more specific through usage Smart IT Engineering Ltd. 67. Keep it Small but No Smaller
- API should satisfy its requirements
68. When in doubt leave it out
- API extended but not curtailed once it is public
Conceptual weight more important than bulk
- Decrease the conceptual weight, i.e. things to learn new
Look for a power-to-weight ratio
- Do more by reusing interfaces, i.e. add implementations targeted at solving different problems
Smart IT Engineering Ltd. 69. Implementation shouldn't impact API
- Implementation details
- Confuse users
70. Inhibit freedom to change implementation Be aware of what is an implementation detail
- Do not over specify the behavior, e.g., hash functions
Don't let implementation details leak into API
- On-disk and on-the-wire formats, exceptions
Smart IT Engineering Ltd. 71. Minimize Accessibility of Everything
- Make classes and members as private as possible
72. Public class should have no public fields other than constants 73. This maximizes information hiding 74. Allows modules to be used, understood, built, tested and debugged independently Smart IT Engineering Ltd. 75. Names Matter API is a Language
- Names should be largely self-explanatory
- Avoid cryptic abbreviations
Be consistent Same word means same thing 76. Be regular strive for symmetry 77. Code should read like prose Smart IT Engineering Ltd. 78. Documentation Matters
- Reuse is something that is far easier to say then to do. Doing
it requires both good design and very good documentation. Even when
we see good deign, which is still infrequently, we won't see the
components reused without good documentation
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- - D. L. Parnas, Software Aging. Proceedings of 16 thInternational Conference on Software Engineering, 1994
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Smart IT Engineering Ltd. 79. Document Religiously
- Document every class, interface, method, constructor, parameter and exception
- Class: What an instance represents
80. Method: Contract between method and its client
- Preconditions, postconditions, side-effects
Document state space very carefully Smart IT Engineering Ltd. 81. Performance Consequence
- Bad decisions can limit performance
82. Do not wrap API to gain performance 83. Be aware of stateful vs stateless requirements Smart IT Engineering Ltd. 84.
- OOP Design Principles
Smart IT Engineering Ltd. 85. Class Design
- Minimize Mutability
- Classes should be immutable
86. If mutable keep state space small, well-defined Subclass only where it makes sense
- Subclass only when is-a relationship exists
87. Prefer composition over inheritence 88. Bad example of inheritance is Properties of Java Document for inheritance else prohibit it Smart IT Engineering Ltd. 89. Method Design
- Reduce need for boilerplate code
- Generally done via cut/copy-and-paste
Don't violate the principle of least astonishment
- User of API should not be surprised by behavior
Fail Fast report errors as soon as possible 90. Provide programmatic access to all data available in string form to avoid user parsing strings Smart IT Engineering Ltd. 91. Method Design
- Overload with care
- Avoid ambiguous overloadings. Preferable no two methods with same number of arguments
92. Just because you can doesn't mean you should Use appropriate parameter and return types
- Favor interface over classes for input
93. Use most specific possible input parameter type 94. Avoid using float (32 bits) in favor of double (64 bits) Smart IT Engineering Ltd. 95. Method Design
- Use consistent parameter ordering across methods
96. Avoid long parameter list
- Three or fewer parameters is ideal
97. Lon list of identically typed params is harmful 98. Break up methods or create helper class to hold parameters Avoid return values that demand exceptional processing
- Return zero-length array or empty collection instead of null.
Smart IT Engineering Ltd. 99. Exception Design
- Throw exceptions to indicate exceptional conditions
- Don't force client to use exceptions for control flow
100. Conversely, don't fail silently Favor unchecked exceptions
- Checked Client must take recovery action
101. Unchecked Programming error Include failure capture information in exceptions Smart IT Engineering Ltd. 102. Conclusion
- API design is a notable and rewarding craft
103. This presentation covered some heuristics of the craft 104. API design is tough 105. Once a API is Public it can evolve but has to support earlier releases Smart IT Engineering Ltd. 106. Questions? Smart IT Engineering Ltd.