private static void Demo3() {
        Stack<Character> st1=new Stack();
        System.out.println("请输入一行字符串：");
        Scanner sc1= new Scanner(System.in);
        String str = sc1.nextLine();
//        System.err.println(str);
        for (int i = 0; i < str.length(); i++) {
            char ch=str.charAt(i);
            switch(ch) {
                case '{':
                case '[':
                case '(':
                    st1.push(ch);
                    break;
                case '}':
                case ']':
                case ')':
                    if (!st1.isEmpty()) {
                        char chx=st1.pop();
                        if ((ch=='{'&&chx!='}')||(ch=='['&&chx!=']')||(ch=='('&&chx!=')')) {
                            System.out.println("Error" + ch+i);
                        }
                    }  else {
                        System.out.println("Error" + ch+i);
                        }
                    break;
                    default:  break;
            }
        }
        if (!st1.isEmpty()) {
            System.out.println("Error" +st1.pop());
        }
//        while (!st1.isEmpty()) {
//            System.out.println(st1.pop());
//        }