application1.java

程序或系统实现的功能：利用数据报设计一个简单的聊天程序.

package packetsenddemo;

import javax.swing.UIManager;
import java.awt.*;
import java.net.*;
import java.io.*;

public class Application1 {
  boolean packFrame = false;

  //Construct the application
  public Application1() {
    Frame1 frame = new Frame1();
    //Validate frames that have preset sizes
    //Pack frames that have useful preferred size info, e.g. from their layout
    if (packFrame) {
      frame.pack();
    }
    else {
      frame.validate();
    }
    //Center the window
    Dimension screenSize = Toolkit.getDefaultToolkit().getScreenSize();
    Dimension frameSize = frame.getSize();
    if (frameSize.height > screenSize.height) {
      frameSize.height = screenSize.height;
    }
    if (frameSize.width > screenSize.width) {
      frameSize.width = screenSize.width;
    }
    frame.setLocation((screenSize.width - frameSize.width) / 2, (screenSize.height - frameSize.height) / 2);
    frame.setVisible(true);
  }
  //Main method
  public static void main(String[] args) {
    String hostname="192.12.0.1";
    try
        {
        System.out.println ("Binding to local port ");
        DatagramSocket socket = new DatagramSocket( );
        System.out.println ("Bound to local port " + socket.getLocalPort( ));
            ByteArrayOutputStream bout = new ByteArrayOutputStream( ); //缺省36字节buffer
            PrintStream pout=new PrintStream(bout);
            pout.print("Greetings!");
            byte[] barray=bout.toByteArray( );
        DatagramPacket packet = new DatagramPacket(barray,barray.length);
        System.out.println ("Looking up hostname"+hostname);
        InetAddress remote_addr =InetAddress.getByName( hostname);
              System.out.println (" hostname resolved as " +remote_addr.getHostAddress() );
              packet.setAddress(remote_addr);//指明目的地址
              packet.setPort(2000); //指明目的端口
              socket.send(packet);
              System.out.println ("Packet sent!");   }
           catch (UnknownHostException uhe)
            {  System.err.println ("Can’t find host - "+hostname);  }
           catch (IOException ioe)
              {	System.err.println ("Error - " + ioe);  }
           }
// new Application1();
  }