给定一个只包含字符’(’，’)’，’{’，’}’，’[‘和’]'的字符串，判断输入字符串是否有效

public class Bracket {

    public static void main(String[] args) {
        String str = "[()]";
        System.out.println(isValid(str));
    }

    // [()]
    public static boolean isValid(String str) {
        Stack stack = new Stack<>();
        Map map = new HashMap();
        map.put(')', '(');
        map.put('}', '{');
        map.put(']', '[');
        char[] chs = str.toCharArray();
        for (Character ch : chs) {
            if (!map.containsKey(ch)) {
                stack.push(ch);
            } else {
                Character item = map.get(ch);
                if (stack.isEmpty() || !item.equals(stack.pop())) {
                    return false;
                }
            }
        }
        return stack.isEmpty();
    }
}