Maximum 69 Number

给一个数字, 6和9可以互换一次, 求得到的最大数字.

class Solution {
    public int maximum69Number (int num) {
        String s = num + "";
        StringBuilder sb = new StringBuilder(s);
        for(int i = 0; i < sb.length(); i++) {
            if(sb.charAt(i) == '6') {
                sb.setCharAt(i, '9');
                break;
            }
        }
        return Integer.valueOf(sb.toString());
    }
}