String:Generate Parentheses

Given n pairs of parentheses, write a function to generate all combinations of well-formed parentheses.
For example, given n = 3, a solution set is:
[
"((()))",
"(()())",
"(())()",
"()(())",
"()()()"
]

public List<String> generateParenthesis(int n) {
        List<String> aryList = new ArrayList<String>();
        getString(aryList, "", 0, 0, n);
        return aryList;
    }
    
    private void getString(List<String> list,String str,int open,int close,int max) {
        if (str.length()==2*max) {
            list.add(str);
            return;
        }
        if (open<max) {
            getString(list, str+"(", open+1, close, max);
        }
        if (close<open) {
            getString(list, str+")", open, close+1, max);
        }
        
    }