Java - Closing socket when reloading class -

so i'm working on server irc, , added config screen can edit port using, have reintialize listen class take effect, have in config class:

listen.closeports(); new listen(); 

and here listen class:

package server.network;  import java.io.bufferedreader; import java.io.ioexception; import java.io.inputstream; import java.io.inputstreamreader; import java.net.serversocket; import java.net.socket;  import server.server; import server.gui.guimain;  public class listen {     private static socket socket = null;     private int port;      public listen() {         try {             port = server.listenport;             @suppresswarnings("resource")             serversocket serversocket = new serversocket(port);             guimain.jta.append("\nserver started , listening messages on port " + port + ".\n");              while(true) {                 socket = serversocket.accept();                 inputstream = socket.getinputstream();                 inputstreamreader isr = new inputstreamreader(is);                 bufferedreader br = new bufferedreader(isr);                 string msg = br.readline();                 guimain.jta.append("received message client: " + msg + "\n");             }         } catch (exception e) {             guimain.jta.append("port " + port + " in use!\n");         } {             try {                 socket.close();             }  catch(exception e) { }         }     }      public static void closeports() {         try {             socket.close();             guimain.jta.append("server closed\n");         } catch (ioexception e) { }     } } 

when start application runs class, opening socket port specified, when try close port here:

public static void closeports() {     try {         socket.close();         guimain.jta.append("server closed\n");     } catch (ioexception e) { } } 

it hangs on socket.close();

and if comment listen.closeports(); out , try reload class , leaving socket open either hangs or runs catch() if port same port in use.

so long story short, how can close socket before reintalizing class , use new port?

here's full exception trows:

java.lang.nullpointerexception     @ server.network.listen.closeports(listen.java:44)     @ server.gui.guisettings.actionperformed(guisettings.java:86)     @ javax.swing.abstractbutton.fireactionperformed(unknown source)     @ javax.swing.abstractbutton$handler.actionperformed(unknown source)     @ javax.swing.defaultbuttonmodel.fireactionperformed(unknown source)     @ javax.swing.defaultbuttonmodel.setpressed(unknown source)     @ javax.swing.plaf.basic.basicbuttonlistener.mousereleased(unknown source)     @ java.awt.component.processmouseevent(unknown source)     @ javax.swing.jcomponent.processmouseevent(unknown source)     @ java.awt.component.processevent(unknown source)     @ java.awt.container.processevent(unknown source)     @ java.awt.component.dispatcheventimpl(unknown source)     @ java.awt.container.dispatcheventimpl(unknown source)     @ java.awt.component.dispatchevent(unknown source)     @ java.awt.lightweightdispatcher.retargetmouseevent(unknown source)     @ java.awt.lightweightdispatcher.processmouseevent(unknown source)     @ java.awt.lightweightdispatcher.dispatchevent(unknown source)     @ java.awt.container.dispatcheventimpl(unknown source)     @ java.awt.window.dispatcheventimpl(unknown source)     @ java.awt.component.dispatchevent(unknown source)     @ java.awt.eventqueue.dispatcheventimpl(unknown source)     @ java.awt.eventqueue.access$200(unknown source)     @ java.awt.eventqueue$3.run(unknown source)     @ java.awt.eventqueue$3.run(unknown source)     @ java.security.accesscontroller.doprivileged(native method)     @ java.security.protectiondomain$1.dointersectionprivilege(unknown source)     @ java.security.protectiondomain$1.dointersectionprivilege(unknown source)     @ java.awt.eventqueue$4.run(unknown source)     @ java.awt.eventqueue$4.run(unknown source)     @ java.security.accesscontroller.doprivileged(native method)     @ java.security.protectiondomain$1.dointersectionprivilege(unknown source)     @ java.awt.eventqueue.dispatchevent(unknown source)     @ java.awt.eventdispatchthread.pumponeeventforfilters(unknown source)     @ java.awt.eventdispatchthread.pumpeventsforfilter(unknown source)     @ java.awt.eventdispatchthread.pumpeventsforhierarchy(unknown source)     @ java.awt.eventdispatchthread.pumpevents(unknown source)     @ java.awt.eventdispatchthread.pumpevents(unknown source)     @ java.awt.eventdispatchthread.run(unknown source) 

the socket variable not assigned until after client makes request. if call closeports() before happens, program still waiting @ socket = serversocket.accept(); , socket.close() throw nullpointerexception because socket still null.

see http://docs.oracle.com/javase/7/docs/api/java/net/serversocket.html#accept() description of serversocket.accept().