Java 8 Functional Programming for Groovy Developers

An introduction to the JDK8 functional model for Groovy developers.

Transcript

1. JDK 8 Functional
   Programming
   …For Groovy Developers
   

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2. John Engelman
   • @johnrengelman
   • github.com/johnrengelman
   • ratpack.io
   • objectpartners.com/category/blog
   

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3. Caveats
   • Scala
   • Clojure
   • Erlang
   • Haskell
   

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4. …Big pile of Salt
   

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6. Questions?
   

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7. public static TransformablePublisher stream(Publisher publisher) {
   return Streams.transformable(subscriber -> require().streamSubscribe((handle) ->
   publisher.subscribe(new Subscriber() {
   @Override
   public void onSubscribe(final Subscription subscription) {
   handle.event(() ->
   subscriber.onSubscribe(subscription)
   );
   }
   @Override
   public void onNext(final T element) {
   handle.event(() -> subscriber.onNext(element));
   }
   @Override
   public void onComplete() {
   handle.complete(subscriber::onComplete);
   }
   @Override
   public void onError(final Throwable cause) {
   handle.complete(() -> subscriber.onError(cause));
   }
   })
   ));
   }
   

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8. java.util.function
   https://docs.oracle.com/javase/8/docs/api/java/util/function/package-summary.html
   

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9. JDK8 Functional Interfaces
   Conceptually, a functional interface has exactly
   one abstract method.
   - https://docs.oracle.com/javase/8/docs/api/java/
   lang/FunctionalInterface.html
   

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10. public interface Supplier {
    T get();
    }
    

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11. Supplier supply() {
    return (() -> {
    return new Foo();
    });
    }
    lambda expression
    parameters list
    body
    

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12. Supplier supply() {
    return (() -> new Foo());
    }
    implicit return
    where have we seen
    that before?
    

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13. Supplier supply() {
    return Foo::new
    }
    method handle
    

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14. Supplier supply() {
    return {
    new Foo()
    }
    }
    Supplier supply() {
    //http://mrhaki.blogspot.com/2015/03/groovy-goodness-
    use-constructor-as.htm
    Foo.metaClass.&invokeConstructor
    }
    

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15. public interface Consumer {
    void accept(T t);
    }
    

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16. Consumer consume() {
    return (val -> System.out.println(val));
    }
    Consumer consumeMethod() {
    return System.out::println;
    }
    

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17. Consumer consume() {
    return { val ->
    println val.name
    }
    }
    Consumer consumeMethod() {
    this.&println
    }
    

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18. public interface Function {
    R appy(T t);
    }
    

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19. Function convert() {
    return (foo -> {
    return new Bar(foo.name);
    });
    }
    Function convertMethod() {
    return Bar::new;
    }
    

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20. Function convert() {
    return { foo ->
    new Bar(foo.name)
    }
    }
    Function convertMethod() {
    Bar.metaClass.&invokeConstructor
    }
    

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21. public interface BiConsumer {
    void accept(T t, U u);
    }
    public interface BiFunction {
    R apply(T t, U u);
    }
    

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22. Where is TriFunction?
    

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23. • BiConsumer
    • BiFunction
    • BinaryOperator
    • BiPredicate
    • BooleanSupplier
    • Consumer
    • DoubleBinaryOperator
    • DoubleConsumer
    • DoubleFunction
    • DoublePredicate
    • DoubleSupplier
    • DoubleToIntFunction
    • DoubleToLongFunction
    • DoubleUnaryOperator
    • Function
    • IntBinaryOperator
    • IntConsumer
    • IntFunction
    • IntPredicate
    • IntSupplier
    • IntToDoubleFunction
    • IntToLongFunction
    • IntUnaryOperator
    • LongBinaryOperator
    • LongConsumer
    • LongFunction
    • LongPredicate
    • LongSupplier
    • LongToDoubleFunction
    • LongToIntFunction
    • LongUnaryOperator
    • ObjDoubleConsumer
    • ObjIntConsumer
    • ObjLongConsumer
    • Predicate
    • Supplier
    • ToDoubleBiFunction
    • ToDoubleFunction
    • ToIntBitFunction
    • ToIntFunction
    • ToLongBiFunction
    • ToLongFunction
    • UnaryOperator
    Java
    • Closure
    Groovy
    

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24. java.util.stream
    https://docs.oracle.com/javase/8/docs/api/java/util/stream/package-summary.html
    

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25. List filter(List foos) {
    return foos.stream()
    .filter(foo ->
    foo.name.equals(“bar")
    ).collect(Collectors.toList());
    }
    List map(List foos) {
    return foos.stream()
    .map(Bar::new).collect(Collectors.toList());
    }
    List distinct(List foos) {
    return foos.stream().distinct().collect(Collectors.toList());
    }
    

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26. List filter(List foos) {
    foos.findAll { foo -> foo.name == 'bar' }
    }
    List map(List foos) {
    foos.collect { new Bar(foo) }
    }
    List distinct(List foos) {
    foos.unique()
    }
    

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27. public static TransformablePublisher stream(Publisher publisher) {
    return Streams.transformable(subscriber -> require().streamSubscribe((handle) ->
    publisher.subscribe(new Subscriber() {
    @Override
    public void onSubscribe(final Subscription subscription) {
    handle.event(() ->
    subscriber.onSubscribe(subscription)
    );
    }
    @Override
    public void onNext(final T element) {
    handle.event(() -> subscriber.onNext(element));
    }
    @Override
    public void onComplete() {
    handle.complete(subscriber::onComplete);
    }
    @Override
    public void onError(final Throwable cause) {
    handle.complete(() -> subscriber.onError(cause));
    }
    })
    ));
    }
    

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28. public static TransformablePublisher stream(Publisher publisher) {
    return Streams.transformable { subscriber ->
    require().streamSubscribe { handle ->
    publisher.subscribe(new Subscriber() {
    @Override
    public void onSubscribe(final Subscription subscription) {
    handle.event {
    subscriber.onSubscribe(subscription)
    }
    }
    @Override
    public void onNext(final T element) {
    handle.event { subscriber.onNext(element) }
    }
    @Override
    public void onComplete() {
    handle.complete(subscriber.&onComplete)
    }
    @Override
    public void onError(final Throwable cause) {
    handle.complete { subscriber.onError(cause) }
    }
    })
    }
    }
    }
    

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29. Default Interface Methods
    • Game changer
    public interface Baz {
    String getName();
    default Bar bar() {
    return new Bar(this);
    }
    }
    Bar interfaceMethod(Baz baz) {
    return baz.bar();
    }
    Bar useInterface() {
    return interfaceMethod(() -> "John");
    }
    becomes a Supplier
    lambda implicitly coerced to
    interface
    

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30. Default Interface Methods
    • Not directly* supported in Groovy
    * Groovy 2.3 introduced Traits which are similar
    

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31. References/More Info
    • https://github.com/danveloper/uberconf2014-
    from-groovy-to-java8/blob/master/from-groovy-to-
    java8.pdf
    • Anything w/ Venkat
    • https://www.youtube.com/watch?
    v=Ee5t_EGjv0A
    

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