Printing *s as triangles in Java?

Question

My assignment in my Java course is to make 3 triangles. One left aligned, one right aligned, and one centered. I have to make a menu for what type of triangle and then input

Answer 1

This is the least complex program, which takes only 1 for loop to print the triangle. This works only for the center triangle, but small tweaking would make it work for other's as well -

import java.io.DataInputStream;

public class Triangle {
    public static void main(String a[]) throws Exception{
        DataInputStream in = new DataInputStream(System.in);

        int n = Integer.parseInt(in.readLine());
        String b = new String(new char[n]).replaceAll("\0", " ");
        String s = "*";
        for(int i=1; i<=n; i++){
            System.out.print(b);
            System.out.println(s);
            s += "**";
            b = b.substring(0, n-i);
            System.out.println();
        }
    }
}