// version 8: import java.util.function.Consumer; import java.util.function.Function; import java.util.List; import java.util.stream.Collectors; import java.util.stream.Stream; class ExtensionMethodFunctional { public void test() { String test = "test"; test = ExtensionMethodFunctional.Extensions.map(test, s -> ExtensionMethodFunctional.Extensions.reverse(s)); ExtensionMethodFunctional.Extensions.consume(test, s -> System.out.println("1: " + s), s -> System.out.println("2: " + s)); ExtensionMethodFunctional.Extensions.consume(test, System.out::println, System.out::println); ExtensionMethodFunctional.Extensions.toList1(Stream.of("a", "b", "c").map(String::toUpperCase)); List<Integer> i2 = ExtensionMethodFunctional.Extensions.toList2(Stream.of("a", "b", "c").map(String::toUpperCase)); } static class Extensions { public static <T, R> R map(T value, Function<T, R> mapper) { return mapper.apply(value); } public static String reverse(String string) { return new StringBuilder(string).reverse().toString(); } @SafeVarargs public static <T> void consume(T o, Consumer<T>... consumer) { for (int i = 0; i < consumer.length; i++) { consumer[i].accept(o); } } public static <T> List<T> toList1(Stream<T> stream) { return (List<T>) stream.collect(Collectors.toList()); } public static <T, U> List<U> toList2(Stream<T> stream) { return null; } } }