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);
			for (int j = 0; j < 9; j++) {
				o =StringUtils.repeat("0", j-i+1); 
			}
			System.out.println(x+o);

		}
	}