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Java 8 Patterns

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Agenda

• Fluent Decorator

• In, Out, In, Out, Shake It All About

• The Lonely Override

• Monad

• Functional Reactive?

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Fluent Decorator

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Comparator

• Building a Comparator before Java 8

• Java 8

Wait! you’re cheating!! It‘s not the reverse order.

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• Use Comparator.reverseOrder

• Use Comparator.comparing

• High order function

Anonymous inner classes were designed to make it easier for Java programmers to pass

around code as data.

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• Order nulls before non-null elements.

• Decorator Pattern

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• Can you figure out this?

Refactor it to nullsFirst(byStringLength())？

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• This would be better!

• last name, and then first name, zip code …

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• Refactor the Decorator pattern itself

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In, Out, In, Out, Shake It All About

《Java 8 Lambdas》

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Logger

• Invoke isLoggable only to check whether calling a method on the Logger

• it uses information from the rental, but does not use information from the customer

• the method is on the wrong object

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Logger

• Invoke isLoggable only to check whether calling a method on the Logger

• it uses information from Logger, but only to

push a value into it

• the block is on the wrong object

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Map

• it uses information from the Map, but only to

push a value into it.

• the block is on the wrong object.

• computeIfPresent、compute、merge …

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The Lonely Override 《Java 8 Lambdas》

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ThreadLocal

• Subclass solely to override a single method

• What you really want is providing a block of code to the method!

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• This wasn't an antipattern before Java 8—it was the idiomatic way of writing this code

• Source code of withInitial

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Monad Patterns

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Optional

• Null sucks, right?

• Optional is trendy now! Optional<Order>

WET

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• Behavioral WET（Write Everything Twice） – You create Optional<T>

– invoke isPresent of Optional<T>

– if true, get and map T to Optional<U>

– if false, return Optional.empty()

• You uses information from Optional<T>, but only to get a Optional<U> from it

• In, Out, In, Out, Shake It All About

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• Let's flatMap repeatedly.

• Using method reference is much clearer.

• Monad? Why is it important? – Enable me to talk about monad right now!!

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• Seriously, a monad is a pattern – You create M<T>

– do actions on M<T>

– get and map T value(s) to M<U>

– do actions on M<U> or else

• Optional Monad

– You create Optional<T>

– invoke isPresent of Optional<T>

– if true, get and map T to Optional<U>

– if false, return Optional.empty()

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• Seriously, a monad is a pattern – You create M<T>

– do actions on M<T>

– get and map T value(s) to M<U>

– do actions on M<U> or else

• Optional Monad

– You create Optional<T>

– invoke isPresent of Optional<T>

– if true, get and map T to Optional<U>

– if false, return Optional.empty()

Hide the boilerplate of computational context

Hide the boilerplate of "if non-null“ logic

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Stream

• for loop hell ... XD

• Call back hell ... XD

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• Stream Monad

– You create Stream<T>

– forEach T element

– map T to Stream<U>

• A simpler example

Hide the boilerplate of nested loops

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• The flatMap operation

4 1

1 2 3 4 5 6

flatMap(List<Integer> to Stream<Integer>)

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CompletableFuture

• A monad is a pattern – You create M<T>

– do actions on M<T>

– get and map T value(s) to M<U>

– do actions on M<U> or else

Hide the boilerplate of computational context

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• Lambda rocks!

• Lambda sucks!!

– You create Future<T>

– wait until T is ready (in another thread)

– use T and the supplied code to create Future<U>

Hide the boilerplate of thread logic. You‘ve done that.

Future<String>

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• CompletableFuture Monad

flatMap

CompletableFuture<String>

CompletableFuture<String>

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• Composable Future

solo

birthdays

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Functional Reactive?

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Functional Reactive Programming

• Reactive

• Data flow

• Propagation of change

• Observer

• Functional

• Asynchronous

• …

WTF?

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Reactive Programming

• A programming paradigm oriented around data flows and the propagation of change

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• If Java supports reactive programming directly, it should ...

• Of course, it's impossible in the language level for Java.

• Model-View-Controller architecture can allow changes in the underlying model to automatically be reflected in the view

(10, 15, 25)

(20, 25, 35)

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Observer

• In MVC, Model-View could be implemented by the Observer pattern.

• Maybe, we can ...

(10, 15, 25)

(20, 25, 35)

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songs

• When things become complex ...

names

albums 1900s

solo artists songs songs songs

songs lengths

nationalities birthdays

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• RxJava Observable

• Look up artist information

• filter、flatMap? map? Stream?

Observable<Artist>

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Functional Reactive Programming

• A programming paradigm for reactive programming using the building blocks of functional programming

• filter、map、reduce、flatMap are

patterns from functional programming

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• Stream builds up computational workflows

over in-memory collections

• Observable composes and sequences

asynchronous and event-based systems. Instead of pulling data out, it gets pushed in

• CompletableFuture is to a single value

• Observable is a sequence of values

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Asynchronous • "that executes in whole seconds is probably

doing something wrong…" - Brendan Eich

• it's 100 milliseconds from research conducted by Robert Miller

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• Make a mountain out of a molehill … XD

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Summary

• Design patterns evolve more and more exquisitely since Java 8.

• Lambda furthers advanced refactoring.

• As the language evolves, so do the idioms that you use when programming.

• A monad is a pattern.

• Functional reactive programming is a mixture of multi patterns and paradigms.

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References

• http://books.gotop.com.tw/v_ACL042200

• http://www.slideshare.net/JustinSDK/jdk8-functional-api

• http://www.slideshare.net/mariofusco/monadic-java

• http://shop.oreilly.com/product/0636920030713.do

• http://en.wikipedia.org/wiki/Reactive_programming

• https://github.com/ReactiveX/RxJava

• https://speakerdeck.com/benjchristensen/functional-reactive-programming-with-rxjava-javaone-2013

• http://shop.oreilly.com/product/9780596802806.do

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Thanks!!

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