heartbeat.java

learning java的源代码。书中每个实例都有相关的代码example。

//file: HeartBeat.java
import java.net.*;
import java.io.*;

public class HeartBeat extends java.applet.Applet {
    String myHost;
    int myPort;

    public void init(  ) {
        myHost = getCodeBase().getHost(  );
        myPort = Integer.parseInt( getParameter("myPort") );
    }

    private void sendMessage( String message ) {
        try {
            byte [] data = message.getBytes(  );
            InetAddress addr = InetAddress.getByName( myHost );
            DatagramPacket pack =
              new DatagramPacket(data, data.length, addr, myPort );
            DatagramSocket ds = new DatagramSocket(  );
            ds.send( pack );
            ds.close(  );
        } catch ( IOException e ) {
            System.out.println( e );  // Error creating socket
        }
    }

    public void start(  ) {
        sendMessage("Arrived");
    }
    public void stop(  ) {
        sendMessage("Departed");
    }
}