Now am working with java application . I have to connect server and client through No-Ip Duc host.Is it possible or not???

Server side code:

ServerSocket ss=new ServerSocket(5223);
System.out.println("Waiting for client");
Socket soc=ss.accept();
System.out.println("Connected");

client side code:

Socket soc=new Socket("rmcsnoiptest.ddns.net", 5223);

This is what i tried.

I simply use code like

InetSocketAddress addr = new InetSocketAddress("XXX.no-ip.biz", 21);
new Socket().connect(addr, 2000);

to connect to a host via No-Ip, and it's just like connecting to any other DNS-registered host. No problem.

The thing that can be fiddly is getting your server accessible if it's behind a router/NAT, but that's not a Java problem :)