最大個数の連続文字を出力

質問:
1つの文字列を指定し、最大数の連続する文字(スペースを含まない)を出力します.
例:
"this is a sentence"=> [t, h, i, s, i, s, a, s, e, n, t, e, n, c, e]
"thiis iss a senntencee"=> [i, s, n, e]
"thiisss iss a senntttenceee"=> [s, t, e]
"thiisss iss a sennnntttenceee"=> [n]

public class Solution {
	public static void main(String[] args) {
		String str = "thiisss iss a senntttenceee";
		ArrayList<Character> list = new Solution().getMostFrequentChars(str);
		for (Character c : list) {
			System.out.print(c + " ");
		}
	}
	public void add(ArrayList<Character> list, int count, int preMaxCount, char current) {
		if (current == ' ') return;
		if (count > preMaxCount) {
			list.clear();
			list.add(current);
		} else if (count == preMaxCount) {
			list.add(current);
		}
	}
	
	public ArrayList<Character> getMostFrequentChars(String str) {
		ArrayList<Character> list = new ArrayList<Character>();
		if (str == null || str.length() == 0) return list;
		char current = str.charAt(0);
		int count = 1;
		int preMaxCount = -1;
		for (int i = 1; i < str.length(); i++) {
			if (str.charAt(i) == current) {
				count++;
			} else {
				if (count >= preMaxCount) {
					add(list, count, preMaxCount, current);
					if (current != ' ') preMaxCount = count;
				}
				current = str.charAt(i);
				count = 1;
			}
		}
		add(list, count, preMaxCount, current);
		return list;
	}
}