Lambdas & Functional Interfaces

import java.util.function.*;
import java.util.Comparator;

public class LambdaDemo {
    public static void main(String[] args) {
        // Lambda syntax variations:
        // (params) -> expression              (single expression, no return needed)
        // (params) -> { statements; return x; } (block body)

        // ── Predicate<T>: T → boolean ────────────────────────────
        Predicate<String> isLong    = s -> s.length() > 5;
        Predicate<String> startsA   = s -> s.startsWith("A");
        Predicate<String> isLongAndA = isLong.and(startsA);    // compose
        Predicate<String> isLongOrA  = isLong.or(startsA);
        Predicate<String> isShort    = isLong.negate();

        System.out.println(isLong.test("Hello"));       // false
        System.out.println(isLong.test("Effective"));   // true
        System.out.println(isLongAndA.test("Alice"));   // false (not long enough)
        System.out.println(isLongAndA.test("Alexandra")); // true

        // ── Function<T,R>: T → R ─────────────────────────────────
        Function<String, Integer> length    = String::length;   // method reference
        Function<String, String>  toUpper   = String::toUpperCase;
        Function<String, Integer> upperLen  = toUpper.andThen(length); // compose
        Function<Integer, Integer> square   = n -> n * n;

        System.out.println(length.apply("Hello"));      // 5
        System.out.println(upperLen.apply("hello"));    // 5
        System.out.println(square.apply(7));            // 49

        // ── Consumer<T>: T → void ────────────────────────────────
        Consumer<String> print     = System.out::println;
        Consumer<String> printUpper = s -> System.out.println(s.toUpperCase());
        Consumer<String> both      = print.andThen(printUpper);  // chain
        both.accept("java");  // prints "java" then "JAVA"

        // ── Supplier<T>: () → T ──────────────────────────────────
        Supplier<String> greeting  = () -> "Hello, Library!";
        Supplier<Double> random    = Math::random;
        System.out.println(greeting.get());

        // ── BiFunction, BiPredicate, BiConsumer ──────────────────
        BiFunction<String, Integer, String> repeat = (s, n) -> s.repeat(n);
        System.out.println(repeat.apply("ha", 3));   // "hahaha"

        // ── Comparator as lambda ──────────────────────────────────
        Comparator<String> byLength = (a, b) -> a.length() - b.length();
        Comparator<String> byLengthThenAlpha = Comparator
            .comparingInt(String::length)
            .thenComparing(Comparator.naturalOrder());
    }
}