Java 中的默认函数式接口

import java.util.List;
import java.util.Random;
import java.util.function.*;

public class Main {
    public static void main(String[] args) {
        // Consumer
        usingConsumer((a) -> System.out.printf("Hello %s", a), "saami");
        System.out.println();
        // Bi-Consumer
        usingBiConsumer((a, b) -> System.out.printf("Name: %s, Age: %d", a, b), "saami", 20);
        System.out.println();
        // Predicate
        var result1 = usingPredicate((a) -> a % 2 == 0, 34);

        if (result1) {
            System.out.println("Even");
        } else {
            System.out.println("Odd");
        }
        // Bi-Predicate
        var result2 = usingBiPredicate((a, b) -> a > b, 12, 22);
        if (result2) {
            System.out.println("Greater");
        } else {
            System.out.println("Lesser");
        }
        // Function
        var result3 = usingFunction((a) -> a + ": this is a number", 5);
        System.out.println(result3);

        // Bi-Function
        var result4 = usingBiFunction((a, b) -> (a > b ? "Greater": "Lesser"), 5, 6);
        System.out.println(result4);

        // Unary-Operator
        var result5 = usingUnaryOperator((a) -> a+5, 10);
        System.out.println(result5);

        // Binary-Operator
        var result6 = usingBinaryOperator((a, b) -> a + b, 12, 32);
        System.out.println(result6);
        Random r = new Random();


        // Function as Predicate
        var result7 = usingFunctionAsPredicate((a) -> a > 99, 999);
        System.out.println(result7);

        // Using Consumer for printing of the list.
        printData((a) -> {
            for (var ele : a) {
                System.out.println(ele);
            }
        } , List.of("S1", "S2", "S3", "S4", "S5"));

        // Using Supplier as a random number generator
        String[] arr = {"saami", "john", "raymond", "puff"};
        System.out.println(getRandomOne(arr, () -> new Random().nextInt(arr.length)));

        // Using Custom Comparator
        System.out.println(usingCustomFunctionalInterface((a, b, c) -> a + b + c, "Saami", " Abbas", " Khan"));

    }

    public static <T> void usingConsumer(Consumer<T> consumer, T a) {
        // Method that takes consumer interface will return void.
        // Can print something constituting 'a'
        consumer.accept(a);
    }

    public static <T, L> void usingBiConsumer(BiConsumer<T, L> biConsumer, T a, L b) {
        biConsumer.accept(a, b);
    }

    public static <T> boolean usingPredicate(Predicate<T> predicate, T a) {
        return predicate.test(a);
    }

    public static <T, L> boolean usingBiPredicate(BiPredicate<T, L> biPredicate, T a, L b) {
        return biPredicate.test(a, b);
    }

    public static <T, R> R usingFunction(Function<T, R> function, T a) {
//        T for the parameter and R for the return type here the return type could be as same as T or
//        could be different like if T is Integer the R could be String 8 + ""
        return function.apply(a);
    }

    public static <T, U, R> R usingBiFunction(BiFunction<T, U, R> biFunction, T a, U b) {
        return biFunction.apply(a, b);
    }

    public static <T> T usingUnaryOperator(UnaryOperator<T> unaryOperator, T a) {
        return unaryOperator.apply(a);
    }

    public static <T> T usingBinaryOperator(BinaryOperator<T> binaryOperator, T a, T b) {
        return binaryOperator.apply(a, b);
    }

    public static <T, R> R usingFunctionAsPredicate(Function<T, R> prediFunction, T a) {
        return prediFunction.apply(a);
    }

    public static <T> void printData(Consumer<T> consumer, T a) {
        /*
         * Prints the data, (List.of()) using a for loop inside of lambda function.
         */
        consumer.accept(a);
    }

    public static String getRandomOne(String[] arr, Supplier<Integer> supplier) {
        return arr[supplier.get()];
    }

    @FunctionalInterface
    interface Concat<T> {
        T concat(T a, T b, T c);
    }
    public static <T> T usingCustomFunctionalInterface(Concat<T> concat, T a, T b, T c) {
        return concat.concat(a, b, c);
    }


}