Triangle.java

/*
Enter height of triangle: 10
*
**
***
****
*****
******
*******
********
*********
**********
*********
********
*******
******
*****
****
***
**
*
*/

import java.util.Optional;
import java.util.Scanner;
import java.util.function.*;
import java.util.stream.IntStream;

public class Triangle {
    private static IntFunction<IntConsumer> f = (m) -> ((IntConsumer) (i) -> IntStream.range(0, i)
            .forEach((n) -> System.out.print("*")))
            .andThen((n) -> System.out.println())
            .andThen((n) -> Optional.ofNullable(n < m ? n : null)
                    .ifPresent((el) -> Triangle.f.apply(m)
                            .andThen((l) -> Triangle.f.apply(0)
                                    .accept(n)).accept(n + 1)));

    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.print("Enter height of triangle: ");
        f.apply(scanner.nextInt()).accept(1);
    }
}