public class Test3 {
        int i = 0;
        int n = 3;
        while (i < n) {
            //打印空格   n-i-1个
            for (int j = 0; j < n - i - 1; j++) {
                System.out.print(" ");
            }
            //打印X i*2+1个
            for (int j = 0; j < i*2 + 1; j++) {
                System.out.print("X");
            }
            //打印换行
            System.out.println( );
            i++;
        }
    }
}

  X
 XXX
XXXXX