Convert integers into english language

Converter.java

	public static String formatNumber(int i) {
		boolean bigger = false;
		StringBuilder sb = new StringBuilder();
		if (i >= 1000) {
			int thousands = i / 1000;
			i -= (thousands * 1000);
			sb.append(formatNumber(thousands));
			sb.append(" thousand ");
			bigger = true;
		}
		if (i >= 100) {
			int hundreds = i / 100;
			i -= (hundreds * 100);
			sb.append(formatNumber(hundreds));
			sb.append(" hundred ");
			bigger = true;
		}
		if (i != 0) {
			if (bigger) {
				sb.append("and ");
			}
			if (i < 10) {
				sb.append(getPrimitiveNumber(i));
			} else if (i < 20) {
				sb.append(getTeenNumber(i));
			} else {
				int tens = i / 10;
				i -= (tens * 10);
				sb.append(getTens(tens));
				if (i != 0) {
					sb.append("-");
					sb.append(getPrimitiveNumber(i));
				}
			}
		}
		return sb.toString();
	}
	
	public static String getTens(int i) {
		switch (i) {
		case 1:
			return "ten";
		case 2:
			return "twenty";
		case 3:
			return "thirty";
		case 4:
			return "forty";
		case 5:
			return "fifty";
		case 6:
			return "sixty";
		case 7:
			return "seventy";
		case 8:
			return "eighty";
		case 9:
			return "ninety";
		}
		throw new IllegalArgumentException();
	}

	public static String getPrimitiveNumber(int i) {
		switch (i) {
		case 1:
			return "one";
		case 2:
			return "two";
		case 3:
			return "three";
		case 4:
			return "four";
		case 5:
			return "five";
		case 6:
			return "six";
		case 7:
			return "seven";
		case 8:
			return "eight";
		case 9:
			return "nine";
		}
		throw new IllegalArgumentException();
	}

	public static String getTeenNumber(int i) {
		switch (i) {
		case 10:
			return "ten";
		case 11:
			return "eleven";
		case 12:
			return "twelve";
		case 13:
			return "thirteen";
		case 14:
			return "fourteen";
		case 15:
			return "fifteen";
		case 16:
			return "sixteen";
		case 17:
			return "seventeen";
		case 18:
			return "eighteen";
		case 19:
			return "nineteen";
		}
		throw new IllegalArgumentException();
	}