JAVA 8 Fuctional Inteface, Method reference and Lambda expression #2

2016/04/30 - [java] - JAVA 8 Fuctional Inteface, Method reference and Lambda expression #1

이번 글에서는 java.util.function 패키지에 선언된 functional interface 중 primitive type을 다루는 functional interface와 그에 대응하는 람다 표현식 및 메소드 레퍼런스에 대해 알아 보겠습니다. 아래 소스를 보시면 BooleanSupplier, ObjDoubleConsumer, ToLongBiFunction 등을 첫번째 인수로 받는 메소드들을 정의하고 호출하는 로직을 구현하였습니다. Functional interface가 인수로 사용될 때 람다 표현식이 어떻게 전달되는지, 어떤 method reference가 전달되는지 확인해 보세요. 보는데 직관적이지 않다면 답글 주세요~!

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package com.jayjaylab.test.testjava.java8;   import java.util.ArrayList; import java.util.List; import java.util.function.*;   /**  * Created by jjkim on 2016. 5. 5..  */ public class TestPrimitiveFunction {     public String addPrefix(double number) {         return "double number : " + number;     }       public <T> void addItemToList(List<T> list, double item) {         //fixme not a good code, use wild card upper bound to restrict generic type.         list.add((T)String.valueOf(item));     }       public <T> void addItemToList(List<T> list, int item) {         list.add((T)String.valueOf(item));     }       public <T> void addItemToList(List<T> list, long item) {         list.add((T)String.valueOf(item));     }       public double sumToDouble(String a, String b) {         return Double.valueOf(a) + Double.valueOf(b);     }       public int sumToInt(String a, String b) {         return Integer.valueOf(a) + Integer.valueOf(b);     }       public long sumToLong(String a, String b) {         return Long.valueOf(a) + Long.valueOf(b);     }       public static void main(String... args) {         TestPrimitiveFunction function = new TestPrimitiveFunction();           // BooleanSupplier         System.out.println(function.tryBooleanSupplier(() -> (true)));         System.out.println(function.tryBooleanSupplier(Thread.currentThread()::isDaemon));           // DoubleBinaryOperator         System.out.println(function.tryDoubleBinaryOperator(                 (l, r) -> (l + r), 10.0d, 2.0d         ));         System.out.println(function.tryDoubleBinaryOperator(                 Double::sum, 10.0d, 2.0d         ));           // DoubleFunction         System.out.println(function.<String>tryDoubleFunction(                 (n) -> {return "double number : " + n;}, 10.0d         ));         System.out.println(function.<String>tryDoubleFunction(                 function::addPrefix, 10.0d         ));           // DoubleToIntFunction         System.out.println(function.tryDoubleToIntFunction(                 (n) -> {return Double.hashCode(n);}, 10.0d         ));         System.out.println(function.tryDoubleToIntFunction(                 Double::hashCode, 10.0d         ));           // ObjDoubleConsumer         List<String> list = new ArrayList<>(10);         function.<List<String>>tryObjDoubleConsumer(                 (l, n) -> {l.add(String.valueOf(n));}, list, 10.0d         );         function.tryObjDoubleConsumer(                 function::<String>addItemToList, list, 10.0d         );           // ObjIntConsumer         function.<List>tryObjIntConsumer(                 (l, n) -> {l.add(String.valueOf(n));}, list, 1         );         function.<List>tryObjIntConsumer(                 function::<String>addItemToList, list, 1         );           // ObjLongConsumer         function.<List>tryObjLongConsumer(                 (l, n) -> {l.add(String.valueOf(n));}, list, 2L         );         function.<List>tryObjLongConsumer(                 function::<String>addItemToList, list, 2L         );           System.out.println("list : " + list);           // ToDoubleBiFunction         System.out.println(function.<String, String>tryToDoubleBiFunction(                 (a, b) -> (Double.valueOf(a) + Double.valueOf(b)), "10.0d", "11.0d"         ));         System.out.println(function.<String, String>tryToDoubleBiFunction(                 function::sumToDouble, "10.0d", "11.0d"         ));           // ToDoubleFunction         System.out.println(function.<String>tryToDoubleFunction(                 (s) -> (Double.valueOf(s)), "10.0d"         ));         System.out.println(function.<String>tryToDoubleFunction(                 Double::valueOf, "10.0d"         ));           // ToIntBiFunction         System.out.println(function.<String, String>tryToIntBiFunction(                 (a, b) -> (Integer.valueOf(a) + Integer.valueOf(b)), "10", "10"         ));         System.out.println(function.<String, String>tryToIntBiFunction(                 function::sumToInt, "10", "10"         ));           // ToIntFunction         System.out.println(function.<String>tryToIntFunction(                 (a) -> (Integer.valueOf(a)), "10"         ));         System.out.println(function.<String>tryToIntFunction(                 Integer::valueOf, "10"         ));           // ToLongBiFunction         System.out.println(function.<String, String>tryToLongBiFunction(                 (a, b) -> (Long.valueOf(a) + Long.valueOf(b)), "10", "20"         ));         System.out.println(function.<String, String>tryToLongBiFunction(                 function::sumToLong, "10", "20"         ));           // ToLongFunction         System.out.println(function.<String>tryToLongFunction(                 (a) -> (Long.valueOf(a)), "100"         ));         System.out.println(function.<String>tryToLongFunction(                 Long::valueOf, "100"         ));     }       public boolean tryBooleanSupplier(BooleanSupplier supplier) {         return supplier.getAsBoolean();     }       public double tryDoubleBinaryOperator(DoubleBinaryOperator operator,                                            double left, double right) {         return operator.applyAsDouble(left, right);     }       public <R> R tryDoubleFunction(DoubleFunction<R> function, double a) {         return function.apply(a);     }       public int tryDoubleToIntFunction(DoubleToIntFunction function, double a) {         return (int)(a % 100);     }       public <T> void tryObjDoubleConsumer(ObjDoubleConsumer<T> consumer, T t, double number) {         consumer.accept(t, number);     }       public <T> void tryObjIntConsumer(ObjIntConsumer<T> consumer, T t, int number) {         consumer.accept(t, number);     }       public <T> void tryObjLongConsumer(ObjLongConsumer<T> consumer, T t, long number) {         consumer.accept(t, number);     }       public <T, U> double tryToDoubleBiFunction(ToDoubleBiFunction<T, U> function,                                              T t, U u) {         return function.applyAsDouble(t, u);     }       public <T> double tryToDoubleFunction(ToDoubleFunction<T> function, T t) {         return function.applyAsDouble(t);     }       public <T, U> int tryToIntBiFunction(ToIntBiFunction<T, U> function, T t, U u) {         return function.applyAsInt(t, u);     }       public <T> int tryToIntFunction(ToIntFunction<T> function, T t) {         return function.applyAsInt(t);     }       public <T, U> long tryToLongBiFunction(ToLongBiFunction<T, U> function, T t, U u) {         return function.applyAsLong(t, u);     }       public <T> long tryToLongFunction(ToLongFunction<T> function, T t) {         return function.applyAsLong(t);     } }