我做了个局域网广播的小程序,就是有问题找不到:

我做了个局域网广播的小程序,就是有问题找不到:
这是异常:
     java.lang.NullPointerException 
at BroadCastServer.<init>(BroadCastServer.java:32) 
at BroadCastServer.main(BroadCastServer.java:159) 
java.lang.NullPointerException 
at BroadCastServer.actionPerformed(BroadCastServer.java:137) 
at javax.swing.Timer.fireActionPerformed(Unknown Source) 
at javax.swing.Timer$DoPostEvent.run(Unknown Source) 
at java.awt.event.InvocationEvent.dispatch(Unknown Source) 
at java.awt.EventQueue.dispatchEvent(Unknown Source) 
at java.awt.EventDispatchThread.pumpOneEventForHierarchy(Unknown Source) 
at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source) 
at java.awt.EventDispatchThread.pumpEvents(Unknown Source) 
at java.awt.EventDispatchThread.pumpEvents(Unknown Source) 
at java.awt.EventDispatchThread.run(Unknown Source) 这是异常地点: 
         super("定时广播系统"); 
try 
{ 
port=5000; 
group=InetAddress.getByName("230.0.0.1"); 
socket.setTimeToLive(1);//这是第32行// 
socket=new MulticastSocket(port); 
socket.joinGroup(group); 
....................... 
public static void main(String[] args)  
{ 
try 
{ 
new BroadCastServer();//这是第159行// 
} 
catch(Exception ee) 
................ 
DatagramPacket packet=null; 
byte data[]=s.getBytes(); 
packet=new DatagramPacket(data,data.length,group,port); 
socket.send(packet);//这是第137行// 
}