If you can use commons-lang3:

	public static void main(String[] args) {
		// Algorithm 1
   	    String o = null;
	    for (int i = 0; i < 10; i++) {
	        String x = StringUtils.repeat("X", i+1);
	        o =StringUtils.repeat("0", 9-i); 
	        System.out.println(x+o);

	    }
	}
StringUtils.repeat is a helper method, this will print a character n times.
So i create a string with n times a `X` and the i do it same with o for the rest and concatinate it for Output.