Butterfly with loops FAROOQ

import java.util.;
public class day4{
public static void butterfly(int n){
//first half
for(int i=1; i<=n; i++)
{
//for stars
for(int j=1; j<=i; j++)
{
System.out.print("");
}
//for spaces
for(int j=1; j<=2*(n-i); j++)
{
System.out.print(" ");
}
//for stars
for(int j=1; j<=i; j++)
{
System.out.print("");
}
System.out.println("");
}
//second half
for(int i=n; i>=1; i--)
{
//for stars
for(int j=1; j<=i; j++)
{
System.out.print("");
}
//for spaces
for(int j=1; j<=2*(n-i); j++)
{
System.out.print(" ");
}
//for stars
for(int j=1; j<=i; j++)
{
System.out.print("*");
}
System.out.println("");
}

}

public static void main(String[] args){
    Scanner sf=new Scanner(System.in);
   System.out.println("Enter rows for butterfly");
    int row=sf.nextInt();
    butterfly(row);
}
}