用于管理Ip的类，没有构造器
1.单例模式
2.根据静态的方法来返回该对象

    public static void main(String[] args){
        
        //gei ip address
        try {
            InetAddress ia = InetAddress.getLocalHost();
            //Get Ip
            String ip = ia.getHostAddress();
            System.out.println(ip);
            
            //Get hostname,
            String hostname = ia.getHostName();
            System.out.println(hostname);
            
        } catch (UnknownHostException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }