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();
	}

};