import java.util.Scanner;
public class Piramide {

    public static void main(String[] args) {

        int num;
        Scanner entrada = new Scanner(System.in);

        System.out.print("Introduce un numero: ");
        num= entrada.nextInt();

        for (int i = 0; i < num; ++i) {

            System.out.println();

            for (int j = 0; j < num-i-1; ++j) {

                }

            for (int j = 0; j < 2*i+1; ++j){

                System.out.print("*");
                }

        }

        System.out.println();

            }
    }

Introduce un numero: 7

*
***
*****
*******
*********
***********
*************