public static void CC17_9_2 () {//PASS
		//use hashtable
		String[] book = {"hello", "world", "descipline", "hello", "dear", 
				"think", "world", "world", "WORLD", "FOOD"};
		String target = "hello";
		target = target.toLowerCase().trim();
		Hashtable<String, Integer> table = new Hashtable<String, Integer>();
		for (int i=0; i<book.length; ++i) {
			String curr = book[i].toLowerCase().trim();
			if ( !table.containsKey(curr) ) {
				table.put(curr, 1);
			}
			else {
				table.put(curr, table.get(curr)+1);
			}
		}
		//then, getFrequency
		if (table == null || target.equals("")) {
			System.out.println("NULL TABLE OR NULL TARGET");
		}
		else {
			if (table.containsKey(target)) {
				System.out.println(table.get(target));
			}
			else {
				System.out.println(0);
			}
		}
	}