括号字符串的有效性和最长有效长度

package 括号字符串的有效性;

public class Test {
    public static void main(String[] args) {
        String str1 = "()";
        String str2 = "())";
        String str3 = "()(";
        String str4 = "()a()";
        System.out.println(isValid(str1));
        System.out.println(isValid(str2));
        System.out.println(isValid(str3));
        System.out.println(isValid(str4));
    }

    public static boolean isValid(String str) {
        if (str == null || str.equals("")) {//str无指向，str指向空字符串
            return false;
        }
        char[] chas = str.toCharArray();
        int status = 0;
        for (int i = 0; i < chas.length; i++) {
            if (chas[i] != '(' && chas[i] != ')') {
                return false;
            }
            if (chas[i] == ')' && --status < 0) {
                return false;
            }
            if (chas[i] == '(') {
                status++;
            }
        }
        return status == 0;
    }
}