DatagramPacket，DatagramSocket

package test;

import java.io.IOException;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.InetAddress;

public class Server {

public static void main(String[] args) throws IOException {
DatagramSocket ds=new DatagramSocket(3000);
String str="Hello";
DatagramPacket dp=new DatagramPacket(str.getBytes(),str.length(),InetAddress.getByName("localhost"),9000);
ds.send(dp);
ds.close();
}

}

package test;

import java.io.IOException;
import java.net.DatagramPacket;
import java.net.DatagramSocket;

public class Client{
public static void main(String args[]) throws IOException{
DatagramSocket ds=new DatagramSocket(9000);
byte b[]=new byte[1024];
DatagramPacket dp=new DatagramPacket(b,1024);
ds.receive(dp);
String str=new String(dp.getData(),0,dp.getLength())+"from"+dp.getAddress().getHostAddress()+":"+dp.getPort();
System.out.println(str);
ds.close();
}

};