17.StringBulider

    public static void main(String[] args) {
//        public StringBuilder append(任意类型):添加数据并返回对象本身
        StringBuilder sb = new StringBuilder();
        sb.append("12");
        sb.append("34");
        sb.append("56");
//        链式编程
        sb.append("78").append("90");
        System.out.println(sb);
        System.out.println(sb.reverse());
    }