如何删除嵌套括号？

数据结构与算法

，。，。，。小菜
括号只有一种，还比较方便

public class Solution {
    public String changeStr(String string) {
        if (string == null || string.length() == 0) {
            return null;
        }
        int counter = 0;
        char[] chars = string.toCharArray();
        StringBuffer sb = new StringBuffer();
        for (int i = 0; i < chars.length; i++) {
            if (chars[i] == '(') {
                counter++;
                continue;
            }
            if (chars[i] == ')') {
                counter--;
                continue;
            }
            sb.append(chars[i]);
        }
        if (counter != 0) {
            return null;
        }
        return sb.toString();
    }
    public static void main(String[] args) {
        Solution solution = new Solution();
        String string = "(1,(2,3),(4,(5,6),7))";
        System.out.println(solution.changeStr(string));
    }
}