编程小白，碰到一道题，感到很迷，求助

Question

每行前输入的空格数让我很迷，找不出规律，求助

Answer 1

public class Triangle {
    //main function
    public static void main(String[] args){
        Triangle p=new Triangle();
        p.printTri(5);
        p.printTri(20);
        p.printTri(10);
        p.printTri(17);

    }

    //print function
    public void printTri(int n) {   
        int i=0,j=2*n-1;
        for (;j-i>=1;i++,j--) {
            for (int k=0;k<2*n-1;k++) {
                if(i<=k&&k<j)
                    System.out.print("*");
                else
                    System.out.print(" ");
            }
            System.out.println();
        }
    }
}