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JAVA 8 LAMBDAS, MONADS && JAVA COLLECTIONS Grzegorz Piwowarek

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GRZEGORZ PIWOWAREK @PIVOVARIT

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GRZEGORZ PIWOWAREK @PIVOVARIT visionsoftondal.com

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Plan: -lambda expressions -java.util.function -monad -Optional -Stream

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lambda expressions (...) -> statement - Anonymous function

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lambda expressions x -> x + 1

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lambda expressions x -> x + 1 - No type information

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lambda expressions x -> x + 1 () -> 42 () -> {return 42;} (x, y) -> {} () -> {}

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method references

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java.util.function

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java.util.function

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Function, BiFunction Consumer extends Function Supplier extends Function Predicate extends Function UnaryOperator extends Function BinaryOperator extends BiFunction

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Function, BiFunction Consumer extends Function Supplier extends Function Predicate extends Function UnaryOperator extends Function BinaryOperator extends BiFunction

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Function, BiFunction Consumer extends Function Supplier extends Function Predicate extends Function UnaryOperator extends Function BinaryOperator extends BiFunction

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Function, BiFunction Consumer extends Function Supplier extends Function Predicate extends Function UnaryOperator extends Function BinaryOperator extends BiFunction

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Function, BiFunction Consumer extends Function Supplier extends Function Predicate extends Function UnaryOperator extends Function BinaryOperator extends BiFunction

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MONAD

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No content

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GOOGLE IMAGES...

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...

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MONAD Design pattern http://got-steam.com/

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Why bother? : Boilerplate -1 Readability +1 Complexity -1 Responsibility -1

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type: M "unit": T -> M "bind": M.bind(T -> M) = M MONAD "bind": M.bind(T -> U)= M

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type: M "unit": T -> M "bind": M bind(T -> M) = M MONAD "bind": M.bind(T -> U)= M

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"bind": M bind(T -> U)= M What if U: M> ?

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"bind": M bind(T -> U)= M What if U: M> ?

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"bind": M bind(T -> U)= M What if U: M> ? http://www.ivanaborovnjak.com/project/box-in-a-box/

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Monads in Java 8 Optional Stream CompletableFuture

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Monads in Java 8 Optional Stream CompletableFuture

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Optional Encapsulation of operations on optional values

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Optional type: M "unit": T -> M "bind": M bind(T -> M) = M

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Optional type: Optional "unit": T -> M "bind": M bind(T -> M) = M

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Optional type: Optional "unit": Optional.ofNullable(), Optional.of() "bind": M bind(T -> M) = M

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Optional type: Optional "unit": Optional.ofNullable(), Optional.of() "bind": Optional.flatMap()

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Filtering an Optional .filter(Predicate)

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Unwrapping an Optional .get() .orElse(T default) .orElseGet(Supplier) .orElseThrow(Supplier) .ifPresent(Consumer)

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Java 7 style

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Java 8 style

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Java 8 style - flatMap

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Java 7,5 style ;)

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Java 7,5 style ;)

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Stream Encapsulation of operations on multiple items

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Stream type: Stream "unit": Stream.of(), Arrays.stream(), Collection.stream() "bind": Stream.flatMap()

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Stream

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Stream

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Stream

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Stream && Optional

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Stream lazy-initialized nonreusable

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intermediate operations .map() .flatMap() .filter() .peek()

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intermediate operations .map() .flatMap() .filter() .peek() Stream not consumed: does not print anything

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Java7

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Java8

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Consuming Stream .forEach(Consumer) .collect() .reduce(BinaryOperator) .allMatch(), anyMatch(), noneMatch() .findFirst(), findAny() .count() .toArray()

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Stream.reduce()

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Collectors .toList(), toMap(), toSet(), toCollection() .minBy(), maxBy() .joining() .partitioningBy() ...and many others

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Collectors.toList()

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Collectors.toMap()

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Collectors.joining()

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Debuggability? IntelliJ IDEA: - v14.0 - partial support - v15.0 - full support

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Stream in APIs BufferedReader.lines() Files.newDirectoryStream() Random.ints() ...

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you want more?

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https://github.com/ jasongoodwin/better-java-monads

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Thank You!

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REFERENCES: -"MONADIC JAVA" BY MARIO FUSCO -"WHAT'S WRONG WITH JAVA 8" BY PIERRE-YVES SAUMONT -WWW.ORACLE.COM -"A FISTFUL OF MONADS" - LEARN YOU A HASKELL FOR GREAT GOOD