Botre Posted April 3, 2016 Posted April 3, 2016 "Functional interfaces provide target types for lambda expressions and method references." https://docs.oracle.com/javase/8/docs/api/java/util/function/package-summary.html In order to further my functional programming adventures I wrote a couple of (arbitrary and overly simplified) examples for almost every interface from java.util.function. Hope these help you understand / recognize the package in question a bit more. package org.dreamstream.sandbox.example.function; import java.util.Random; import java.util.function.*; public class FunctionPackageExample { public static void main(String[] args) { /** * Predicate * Represents a predicate (boolean-valued function) of one or two arguments. */ final Predicate<String> IS_EMPTY = s -> s.isEmpty(); System.out.println(IS_EMPTY.test("")); // = true final BiPredicate<String, String> ARE_EQUAL = (s1, s2) -> s1.equals(s2); System.out.println(ARE_EQUAL.test("Test1", "Test2")); // = false final IntPredicate IS_EVEN = i -> i % 2 == 0; System.out.println(IS_EVEN.test(2)); // = true final LongPredicate CAN_TRUNCATE_TO_INT = l -> l >= Integer.MIN_VALUE && l <= Integer.MAX_VALUE ; System.out.println(CAN_TRUNCATE_TO_INT.test(Integer.MAX_VALUE + 1l)); // = false final DoublePredicate IS_CLOSE_TO_ZERO = d -> Math.abs(d) < 2 * Double.MIN_VALUE; System.out.println(IS_CLOSE_TO_ZERO.test(0.0)); // = true /** * Function * Represents a function that accepts one or two arguments and produces a result. */ Function<String, Integer> CAST = s -> Integer.parseInt(s); System.out.println(CAST.apply("1") + 2); // = 3 BiFunction<Integer, Integer, String> SUM_TO_STRING = (i1, i2) -> Integer.toString(i1 + i2); System.out.println(SUM_TO_STRING.apply(5, 10) + "Hi"); // = 15Hi IntFunction<Double> AS_DOUBLE = i -> i * 1d; System.out.println(AS_DOUBLE.apply(1)); // = 1.0 LongFunction<Integer> AS_INTEGER = l -> (int)l; System.out.println(AS_INTEGER.apply(Long.MAX_VALUE)); // = -1 DoubleFunction<Integer> DOUBLE_AS_INTEGER = d -> (int)d; System.out.println(DOUBLE_AS_INTEGER.apply(2.5)); // = 2 /** * Consumer * Represents an operation that accepts one or two input arguments and returns no result. */ final Consumer<String> PRINT = s -> System.out.println(s); PRINT.accept("Yes / No"); // = "Yes / No" final BiConsumer<String, Integer> PRINT_STRING_AND_INTEGER = (s, i) -> System.out.println("String: " + s + " Ingeger: " + i); PRINT_STRING_AND_INTEGER.accept("Test", 3); // = "String: Test Ingeger: 3" final IntConsumer PRINT_I = i -> System.out.println(i); PRINT_I.accept(3); // = 3 final LongConsumer PRINT_L = l -> System.out.println(l); PRINT_L.accept(2); // = 2 final DoubleConsumer PRINT_D = d -> System.out.println(d); PRINT_D.accept(2.5); // = 2.5 final ObjIntConsumer<String> PRINT_I_S = (s, i) -> System.out.println(s + " " + i); PRINT_I_S.accept("A", 1); // = "A 1" final ObjLongConsumer<String> PRINT_L_S = (s, l) -> System.out.println(s + " " + l); PRINT_L_S.accept("B", 2); // = "B 2" final ObjDoubleConsumer<String> PRINT_D_S = (s, d) -> System.out.println(s + " " + d); PRINT_D_S.accept("C", 2.5); // = "C 2.5" /** * Supplier * Represents a supplier of results of a specific type. */ final Supplier<Double> SUPPLY_RANDOM = () -> Math.random(); System.out.println(SUPPLY_RANDOM.get()); // = A double value with a positive sign, greater than or equal to 0.0 and less than 1.0 final BooleanSupplier SUPPLY_TRUE = () -> true; System.out.println(SUPPLY_TRUE.getAsBoolean()); // = true final IntSupplier SUPPLY_EVEN = () -> new Random().nextInt() & -2; System.out.println(SUPPLY_EVEN.getAsInt()); // = An even int value final LongSupplier SUPPLY_ZERO = () -> 0; System.out.println(SUPPLY_ZERO.getAsLong()); // = 0 final DoubleSupplier SUPPLY_MIN = () -> Double.MIN_VALUE; System.out.println(SUPPLY_MIN.getAsDouble()); // = 4.9E-324 /** * ToNumber * Represents functions that accept one or two two arguments and produces a value of a number-type. */ final ToIntFunction<String> CHARACTER_COUNT = s -> s.length(); System.out.println(CHARACTER_COUNT.applyAsInt("Five5")); // = 5 final ToIntBiFunction<String, String> SUM_CHARACTER_COUNT = (s1, s2) -> s1.length() + s2.length(); System.out.println(SUM_CHARACTER_COUNT.applyAsInt("AB", "C")); // = 3 final ToLongFunction<String> THOUSAND_TIMES_CHARACTER_COUNT = s -> s.toCharArray().length * 1000l; System.out.println(THOUSAND_TIMES_CHARACTER_COUNT.applyAsLong("Five5")); // = 5000 final ToLongBiFunction<Long, String> SUM = (l, s) -> l + Integer.parseInt(s); System.out.println(SUM.applyAsLong(300l, "1")); // = 301 final ToDoubleFunction<String> HALF_CHARACTER_COUNT = s -> s.length() / 2d; System.out.println(HALF_CHARACTER_COUNT.applyAsDouble("One")); // = 1.5 final ToDoubleBiFunction<String, String> AVERAGE_CHARACTER_COUNT = (s1, s2) -> (s1.length() + s2.length()) / 2d; System.out.println(AVERAGE_CHARACTER_COUNT.applyAsDouble("One", "Five")); // = 3.5 /** * Operator * Represents an operation on one or two operands of the same type, producing a result of the same type as the operand(s). */ final UnaryOperator<String> REVERSE = s -> new StringBuilder(s).reverse().toString(); System.out.println(REVERSE.apply("test")); // = "tset" final BinaryOperator<String> CONCAT = (s1, s2) -> s1.concat(s2); System.out.println(CONCAT.apply("Hello, ", "World!")); // = "Hello, World!" final IntUnaryOperator DOUBLE = i -> i * 2; System.out.println(DOUBLE.applyAsInt(5)); // = 10 final IntBinaryOperator INTEGER_SUM = (i1, i2) -> i1 + i2; System.out.println(INTEGER_SUM.applyAsInt(9, 3)); // = 12 final LongUnaryOperator NEGATE = l -> -l; System.out.println(NEGATE.applyAsLong(1)); // = -1 final LongBinaryOperator DIFFERENCE = (l1, l2) -> l1 - l2; System.out.println(DIFFERENCE.applyAsLong(1, 3)); // = -2 final DoubleUnaryOperator HALF = d -> d / 2; System.out.println(HALF.applyAsDouble(5)); // = 2.5 final DoubleBinaryOperator AVERAGE = (d1, d2) -> (d1 + d2) / 2; System.out.println(AVERAGE.applyAsDouble(1.0, 2.0)); // = 1.5 } }
FrostBug Posted April 3, 2016 Posted April 3, 2016 Interedasting. Read a lot about this, but haven't really ever had the need to use them. final IntConsumer PRINT_I = i -> System.out.println(i); PRINT_I.accept(3); // = 3 final LongConsumer PRINT_L = l -> System.out.println(l); PRINT_L.accept(2); // = 2 final DoubleConsumer PRINT_D = d -> System.out.println(d); PRINT_D.accept(2.5); // = 2.5 I reckon these could also be written as final IntConsumer PRINT_I = System.out::println; PRINT_I.accept(3); // = 3 final LongConsumer PRINT_L = System.out::println; PRINT_L.accept(2); // = 2 final DoubleConsumer PRINT_D = System.out::println; PRINT_D.accept(2.5); // = 2.5 For the same effect. 1
Botre Posted April 3, 2016 Author Posted April 3, 2016 Interedasting. Read a lot about this, but haven't really ever had the need to use them. final IntConsumer PRINT_I = i -> System.out.println(i); PRINT_I.accept(3); // = 3 final LongConsumer PRINT_L = l -> System.out.println(l); PRINT_L.accept(2); // = 2 final DoubleConsumer PRINT_D = d -> System.out.println(d); PRINT_D.accept(2.5); // = 2.5 I reckon these could also be written as final IntConsumer PRINT_I = System.out::println; PRINT_I.accept(3); // = 3 final LongConsumer PRINT_L = System.out::println; PRINT_L.accept(2); // = 2 final DoubleConsumer PRINT_D = System.out::println; PRINT_D.accept(2.5); // = 2.5 For the same effect. Shame on me sensei but I have not yet read up on method references. It's on my TODO list for next week though
