람다 & 함수형 인터페이스

Java code

import java.util.function.*;

public class Lambdas {
    public static void main(String[] args) {
        // 기본 람다
        Runnable r = () -> System.out.println("실행!");
        r.run();

        // Function<T, R> — T 입력, R 출력
        Function<String, Integer> strLen = String::length;
        Function<Integer, Integer> double_ = n -> n * 2;
        Function<String, Integer> composed = strLen.andThen(double_);
        System.out.println(composed.apply("Hello")); // 10

        // Predicate<T> — boolean 반환
        Predicate<String> notEmpty = s -> !s.isEmpty();
        Predicate<String> longStr  = s -> s.length() > 5;
        Predicate<String> both     = notEmpty.and(longStr);
        System.out.println(both.test("Hello World")); // true

        // Consumer<T> — 반환 없음
        Consumer<String> print = System.out::println;
        Consumer<String> printUpper = s -> System.out.println(s.toUpperCase());
        print.andThen(printUpper).accept("java");

        // Supplier<T> — 인자 없음
        Supplier<String> greeting = () -> "Hello, Java!";
        System.out.println(greeting.get());

        // BiFunction<T, U, R>
        BiFunction<Integer, Integer, Integer> add = Integer::sum;
        System.out.println(add.apply(3, 4)); // 7

        // UnaryOperator, BinaryOperator
        UnaryOperator<Integer>   square = n -> n * n;
        BinaryOperator<Integer> multiply = (a, b) -> a * b;
        System.out.println(square.apply(5));    // 25
        System.out.println(multiply.apply(3,4)); // 12
    }
}