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Java day2016 "Reinventing design patterns with java 8"
- 1. www.luxoft.com REINVENTING DESIGN PATTERNS WITH JAVA8 Alexander Pashynskiy Java Day 2016
- 2. www.luxoft.com About me: • Lead Software Engineer in Luxoft • More then 6 years experience in Java • Agile and Lean practicioner • Pragmatic and product oriented engineer • Still learning and learn Email: hunter041@gmail.com Twitter: @apashinskiy_cv Alexander Pashinskiy
- 3. www.luxoft.com It’s my own experience… Disclaimer
- 9. www.luxoft.com Not only Many, many more ...
- 10. www.luxoft.com • OOP (Resource acquisition is initialization, Servant, DI, Pool Objects, Null object …) • FP (Functions, Monads, Lenz, Curring, …) • Concurrency (Double-checked locking, Read-write lock, Thread-specific storage, …) • Domain Specific (security, money, …) • and many, many more
- 11. www.luxoft.com • Problem - Solution pairs • Similar (or same) solution - different intention (Strategy, State …) • inheritance - composition game (OOP) • Adding level of indirection • Almost always trade-off Design Patterns:
- 12. www.luxoft.com • 1994 year • For C++ • OOP Two main principles: • "Program to an interface, not an implementation." • "Favor object composition over class inheritance." Sad:( Some GoF patterns do not stick to this principles
- 14. www.luxoft.com Lambda -> lightwaight design tool
- 16. www.luxoft.com Template method Type: behavioral Definition: Define the skeleton of an algorithm in an operation, deferring some steps to subclasses. Template Method lets subclasses redefine certain steps of an algorithm without changing the algorithm's structure.
- 17. www.luxoft.com • Not only for data • BLSP • Violates “Single Responsibility” and encapsulation • High Coupling • Future behavior and frameworks inhereted • Broken “protected” in Java • Big hierarchy produces hell Inheritance
- 18. www.luxoft.com Template method • Inheritance is evil • Use composition • Part of an algorithm can be passed as a function • Utilize basic functional interfaces • Use function composition if possible
- 19. www.luxoft.com Template method inheritance -> composition -> function composition
- 20. www.luxoft.com Template method g.filterMailBox(f) * Not strongly mathematical composition (contains ‘if’ logic)
- 23. www.luxoft.com Decorator Type: structural Definition: Attach additional responsibilities to an object dynamically. Decorators provide a flexible alternative to subclassing for extending functionality.
- 24. www.luxoft.com Decorator just a function composition g.andThen(f)
- 27. www.luxoft.com Chain of Responsibility Type: behavioral Definition: Avoid coupling the sender of a request to its receiver by giving more than one object a chance to handle the request. Chain the receiving objects and pass the request along the chain until an object handles it.
- 28. www.luxoft.com Chain of Responsibility chain of function composition andThen andThen andThen andThen andThen
- 31. www.luxoft.com Adapter Type: structural Definition: Convert the interface of a class into another interface clients expect. Adapter lets classes work together that couldn't otherwise because of incompatible interfaces.
- 32. www.luxoft.com Adapter • Utilise basic functional interfaces • Functional interfaces are interchangable • For different numbers of parameters - partially applied function
- 33. www.luxoft.com Partially applied function IntBinaryOperator add = (x, y) -> x + y ; IntUnaryOperator add5 = x -> add.applyAsInt(x, 5); Partial application - process of transforming a function into a function with less parameters.
- 34. www.luxoft.com Partially applied function Supported by java - :: operator ToIntFunctiont<String> stringLength = String::length; IntFunction<String> helloSubstring = "hello"::substring;
- 35. www.luxoft.com Partial application • allows to set some (not all) parameters • let the other parameters to be set later • partially applied function can be reused and composed • Powerful decoupling tool
- 38. www.luxoft.com Proxy Type: structural Definition: Provide a surrogate or placeholder for another object to control access to it.
- 39. www.luxoft.com Proxy • Resource managing • Transactions • Logging • and more ...
- 40. www.luxoft.com Libs to create Proxy • java.lang.reflect.Proxy • Byte Buddy • cglib • javassist
- 41. www.luxoft.com Proxy • function composition • wrap a lambda • inverse of control – resource leasing
- 45. www.luxoft.com Strategy Type: behavioral Definition: Define a family of algorithms, encapsulate each one, and make them interchangeable. Strategy lets the algorithm vary independently from clients that use it.
- 46. www.luxoft.com Strategy library of classes -> library of functions
- 49. www.luxoft.com Iterator Type: behavioral Definition: Provide a way to access the elements of an aggregate objects equentially without exposing its underlying representation.
- 50. www.luxoft.com Iterator external iterator -> internal iterator
- 51. www.luxoft.com Iterator • collections have internal foreach() • streams everywhere • if not - implement Spliterator
- 54. www.luxoft.com Builder Type: creational Definition: Separate the construction of a complex object from its representation so that the same construction process can create different representations.
- 55. www.luxoft.com Builder • classic runtime builder • classic reusable builder (a lot of boiler-plate) • or just use a consumer if applicable - no boiler-plate - reusable (function composition) - chaining DSL - consumer has internal control on objet
- 56. www.luxoft.com Builder say me how -> I will build as you want
- 58. www.luxoft.com Function composition f: a -> b g: b -> c h: c -> d f g h => andThan()° °
- 59. www.luxoft.com Function composition f: a -> b g: b -> c h: c -> d f g h => andThan()° ° f: a -> Mb g: b -> Mc h: c -> Md Mb – container for b
- 60. www.luxoft.com Function composition f: a -> b g: b -> c h: c -> d f g h => andThan()° ° f: a -> Mb g: b -> Mc h: c -> Md f g h => flatMap()° °
- 62. www.luxoft.com Monad Represents (2 and more) states as a unified value in order to compose transformations [User | Error] -> validate1 -> [User | Error] -> validate2 -> [User | Error ] -> get User Error User of
- 63. www.luxoft.com Monad • Puts a value in a computational context
- 64. www.luxoft.com Monad • Puts a value in a computational context • Function composition on steroids
- 65. www.luxoft.com Monad • Puts a value in a computational context • Function composition on steroids • Programmable semicolon
- 66. www.luxoft.com Monad • Puts a value in a computational context • Function composition on steroids • Programmable semicolon • Chainable container
- 67. www.luxoft.com Monad f: a -> Ma g: a -> Ma h: a -> Ma f g h => flatMap° ° Function composition: f: a -> Mb g: b -> Mc h: c -> Md
- 68. www.luxoft.com Monad interface Monad<A> { Monad<A> unit(A a); Monad<B> flatMap(Function<A, Monad<B>> f); }
- 69. www.luxoft.com Monad interface Monad<A> { Monad<A> unit(A a); Monad<B> flatMap(Function<A, Monad<B>> f); default Monad<B> map(Function<A, B> f) { return flatMap(v -> unit(f.apply(v))); } }
- 70. www.luxoft.com Monad interface Monad<A> { Monad<A> unit(A a); Monad<B> flatMap(Function<A, Monad<B>> f); default Monad<B> map(Function<A, B> f) { return flatMap(v -> unit(f.apply(v))); } } Monad composition Function application
- 71. www.luxoft.com Monad • Hide complexity • Encapsulate implementation details • Allow composability • Increase redability • Reduce code duplication
- 72. www.luxoft.com Already in Java 8 • Optional • Stream • CompleatableFuture
- 75. www.luxoft.com Visitor Type: behavioral Definition: Represent an operation to be performed on the elements of an object structure. Visitor lets you define a new operation without changing the classes of the elements on which it operates.
- 76. www.luxoft.com Visitor • Rarely used pattern • Can be replaced by pattern matching • Reuse general implementation
- 77. www.luxoft.com Visitor interface Visitor<T> { T visit(Square element); T visit(Circle element); T visit(Rectangle element); } def visit(e: Element): T = e match { case Square => do1(); case Circle => do2(); case Rectangle => do3(); }
- 79. www.luxoft.com Paradigm shift: • object centric -> function centric • function composition reduce complexity • data to code -> code to data • external -> internal (mechanic incapsulation)
- 80. www.luxoft.com • functions • higher order function • function composition • partially applied functions • monads • pattern matching • … New Designers Toolbox
- 81. www.luxoft.com Design Patterns communication tool rather then implementation guide
- 82. www.luxoft.com “In the book we only tell when to apply pattern, but we never talk about when to remove a pattern. Removing a pattern can simplify a system and a simple solution should almost always win. Coming up with a simple solutions is the real challenge.” E.Gamma
- 83. www.luxoft.com • no silver bullet • OOP is alive • GoF “Design Patterns” is still valid • you just have additional design tools • almost always trade-off • use your mind And remember: