DagagramSocket运行问题

lihaifeng0412 2008-04-03 02:03:04

color=#FF6600]这段客户端程序为什么老是提示错误[/color]



package communicationClient;

import java.awt.*;

import java.awt.event.*;

import java.applet.*;

import javax.swing.*;

import java.net.*;

import java.io.*;

public class CommunicationClient extends Applet{

	

	boolean isStandalone=false;

	JLabel jlabel1=new JLabel();

	JLabel jlabel2=new JLabel();

	JTextField jtextfield1=new JTextField();

	JTextArea jtextarea1=new JTextArea();

	

	private  DatagramSocket sendSocket,receiveSocket;

	private  DatagramPacket sendPacket,receivePacket;

	

	public String getParameter(String key,String def){

		return isStandalone ? System.getProperty(key,def) : (getParameter(key)!=null ? getParameter(key) :def);

	}

	public void init(){

		

		try{

			jbInit();

		}catch(Exception e){

			e.printStackTrace();

		}

	}

	

	private void jbInit() throws Exception{

		jlabel1.setText("通讯记录 : ");

		jlabel1.setBounds(new Rectangle(16,9,68,27));

		setLayout(null);

		jtextarea1.setText("你好!");

		jtextarea1.setBounds(new Rectangle(15,48,349,59));

		

	    jlabel2.setText("输入通讯内容:");

	    jlabel2.setBounds(new Rectangle(17,125,92,37));

	    jtextfield1.setText("通讯内容:");

	    jtextfield1.setBounds(new Rectangle (127,129,244,33));

	    jtextfield1.addActionListener(new java.awt.event.ActionListener(){

	    	public void actionPerformed(ActionEvent e){

	    		jtextfield1_actionPerformed(e);

	    	}

	    });

	    

	    

	    this.add(jlabel1,null);

	    this.add(jtextarea1,null);

	    this.add(jlabel2,null);

	    this.add(jtextfield1,null);

	    	    		

	}

	public void start(){

	  this.waitForPackets();

	}

	public String getAppletInfo(){

		return "Applet Infomation";

	}

	public String[][] getParameterInfo(){

		return null;

	}

	

	public void waitForPackets(){

		try

		{

	    sendSocket=new DatagramSocket();

		receiveSocket=new DatagramSocket(8001);		

	    } 

	    catch(SocketException e){

	    	jtextarea1.append("不能打开数据Socket,或数据Socket 无法与指定端口连接!");

	    }

	    while(true){

	    	try{

	    		byte[] buf= new byte[100];

	    		receivePacket=new DatagramPacket(buf,buf.length);

	    		receiveSocket.receive(receivePacket);

	    		jtextarea1.append("\n 服务器 :\t");

	            byte[] data=receivePacket.getData();

	            String receivedString=new String(data);

	            jtextarea1.append(receivedString);

	    	   }

	    	   catch(IOException e){

	    	   	jtextarea1.append("网络通讯出现错误,问题在" +e.toString());

	    	   }

	    }

	   

    }

    

    public static void main(String[] args){

    	CommunicationClient applet=new CommunicationClient();

    	applet.isStandalone=true;

    	Frame frame;

    	frame=new Frame(){

    		protected void processWindowEvent(WindowEvent e){

    			super.processComponentEvent(e);

    			if(e.getID()==WindowEvent.WINDOW_CLOSING){

    				System.exit(0);

    			}

    		}

    		public synchronized void setTitle(String title){

    			super.setTitle(title);

    			this.enableEvents(AWTEvent.WINDOW_EVENT_MASK);

    		}

    	};

    	

    	frame.setTitle("Applet Frame");

    	frame.add(applet,BorderLayout.CENTER);

    	applet.init();

    	applet.start();

    	frame.setSize(400,320);

    	Dimension d=Toolkit.getDefaultToolkit().getScreenSize();

    	frame.setLocation((d.width - frame.getSize().width)/2,(d.height - frame.getSize().height)/2);

		frame.setVisible(true);

     }

     

     void jtextfield1_actionPerformed(ActionEvent e){

     	try{

     		jtextarea1.append("\n客户端 : ");

     		String string=jtextfield1.getText();

     		jtextarea1.append(string);

     		byte[] databyte=new byte[100];

     		string.getBytes(0,string.length(),databyte,0);

     		sendPacket=new DatagramPacket(databyte,string.length(),InetAddress.getByName("192.168.13.47"),8000);

     		sendSocket.send(sendPacket);

     	}

     	catch(IOException e1){

     		jtextarea1.append("网络通讯出现错误,问题在 "+e1.toString());

     	}

     }

}

浏览器运行时JAVA控制台总提示:



java.lang.NullPointerException

	at communicationClient.CommunicationClient.waitForPackets(CommunicationClient.java:78)

	at communicationClient.CommunicationClient.start(CommunicationClient.java:56)

	at sun.applet.AppletPanel.run(Unknown Source)

	at java.lang.Thread.run(Unknown Source)

Exception in thread "thread applet-communicationClient\CommunicationClient.class" java.lang.NullPointerException

	at sun.plugin.util.GrayBoxPainter.showLoadingError(Unknown Source)

	at sun.plugin.AppletViewer.showAppletException(Unknown Source)

	at sun.applet.AppletPanel.run(Unknown Source)

	at java.lang.Thread.run(Unknown Source)

这到底怎么回事啊!
按照一般窗口运行时提示



Exception in thread "main" java.lang.NullPointerException

        at communicationClient.CommunicationClient.waitForPackets(CommunicationC

lient.java:78)

        at communicationClient.CommunicationClient.start(CommunicationClient.jav

a:56)

        at communicationClient.CommunicationClient.main(CommunicationClient.java

:111)

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急!!!!!!!!!!!!!!!!!!!!各位高手帮忙啊!不胜感激!

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