Reverse Words in a String

Given an input string, reverse the string word by word.

• What constitutes a word?
  A sequence of non-space characters constitutes a word.
• Could the input string contain leading or trailing spaces?
  Yes. However, your reversed string should not contain leading or trailing spaces.

How about multiple spaces between two words?Reduce them to a single space in the reversed string.In this question, I implemented a method called getFirstWord. This method is used to remove the spaces, like the trim method, and get the first word in the input string, save it to the arraylist, and then return the left string. We could use this method to implement tokenizing. You could use the tonikenizer and trim for jave, but that seems cheating......

public class Solution {
    public String reverseWords(String s) {
		ArrayList<String> result = new ArrayList<String>();
		String resultString = "";
		if (s.length() == 0) {
			return resultString;
		}
		String remainingWords = s;
		while(remainingWords != null) {
			remainingWords = getFirstWord(remainingWords, result);
		}
		if (result.size() == 0) {
			return resultString;
		}
		Collections.reverse(result);
		for(String str:result) {
			resultString += " " + str;
		}
		return resultString.substring(1);
    }
	public String getFirstWord(String str, ArrayList<String> words) {
		String word = "";
		int i;
		int length = str.length();
		for (i = 0; i < length; i++) {
			if (str.charAt(i) != ' ') {
				break;
			}
		}
		if (i == length) {
			return null;
		}
		else {
			String remains = str.substring(i);
			int remainLength = remains.length();
			for (i = 0; i < remainLength; i++) {
				if (remains.charAt(i) != ' ') {
					word += remains.charAt(i);
				}
				else {
					break;
				}
			}
			words.add(word);
			if (i == remainLength) {
				return null;
			}
			else {
				return remains.substring(i);
			}
		}
	}
}