rumus :


public class bintang {
public static void main(String[]args){
int barisx=6;
int btg=1;
for(int i=barisx; i>=1; i--){
for(int j=1; j<=i; j++){ System.out.print(' '); } for(int k=1; k<=btg; k++){ System.out.print('*'); } btg+=2; System.out.println(); } btg-=4; for(int i=1; i<=barisx-1; i++){ for(int j=1; j<=i+1; j++){ System.out.print(' '); } for(int k=btg; k>=1; k--){
System.out.print('*');

}
btg-=2;
System.out.println();
}
}
}