How to make custom Java/JavaFX console? -

it's necessary make custom console. have following code:

public class console extends outputstream{  private console(resourcebundle resourcebundle) throws ioexception {     fxmlloader loader = new fxmlloader(this.getclass().getresource("console.fxml"), resourcebundle);     controller = loader.getcontroller();     scene scene = new scene((parent) loader.load());     stage = new stage();     stage.setscene(scene);     show(); }  @override public void write(int b) throws ioexception {     controller.append(b); }  public static console getinstance(resourcebundle resourcebundle) {     if (console == null) {         try {             console = new console(resourcebundle);         } catch (ioexception e) {             e.printstacktrace();  //to change body of catch statement use file | settings | file templates.         }     }     return console; }  public void show() {     stage.show(); }  private static console console = null; private consolecontroller controller; private stage stage; } 

controller file:

public class consolecontroller implements initializable {  @override public void initialize(url url, resourcebundle resourcebundle) { }  @fxml public void append(int i) {     textarea.appendtext(string.valueof((char) i)); }  @fxml private textarea textarea; } 

and these called 'start()':

    @override public void start(stage primarystage) throws ioexception {     ...     system.seterr(new printstream(console.getinstance(rb))); } 

during exception nothing printed in textarea of console.fxml, following exception thrown:

exception in thread "javafx application thread" exception: java.lang.nullpointerexception thrown uncaughtexceptionhandler in thread "javafx application thread"

what doing wrong?

------edit--------

after understanding it's necessary use several threads have following code:

public class console{ private console(resourcebundle resourcebundle) throws ioexception {     fxmlloader loader = new fxmlloader(this.getclass().getresource("console.fxml"), resourcebundle);     parent root = (parent) loader.load();     controller = loader.getcontroller();     scene scene = new scene(root);     stage = new stage();     stage.setscene(scene);     show();      if (erroroutputthread != null) {         erroroutputthread.interrupt();         try {             erroroutputthread.join();         } catch (interruptedexception e) {             e.printstacktrace();  //to change body of catch statement use file | settings | file templates.         }         erroroutputthread = null;     }      if (outoutputthread != null) {         outoutputthread.interrupt();         try {             outoutputthread.join();         } catch (interruptedexception e) {             e.printstacktrace();  //to change body of catch statement use file | settings | file templates.         }         outoutputthread = null;     }      system.err.flush();     system.out.flush();      outpipedinputstream = new pipedinputstream();     outpipedoutputstream = new pipedoutputstream(outpipedinputstream);     system.setout(new printstream(outpipedoutputstream));      errorpipedinputstream = new pipedinputstream();     errorpipedoutputstream = new pipedoutputstream(errorpipedinputstream);     system.seterr(new printstream(errorpipedoutputstream));      outoutputthread = new thread(new consolestream(outpipedinputstream, "out"));     outoutputthread.setdaemon(true);     outoutputthread.start();      erroroutputthread = new thread(new consolestream(errorpipedinputstream, "error"));     erroroutputthread.setdaemon(true);     erroroutputthread.start();      controller.appendtext("start console");  }  public static console getinstance(resourcebundle resourcebundle) {     if (console == null) {         try {             console = new console(resourcebundle);         } catch (ioexception e) {             e.printstacktrace();  //to change body of catch statement use file | settings | file templates.         }     }     return console; }  public void show() {     stage.show(); }  private class consolestream implements runnable {     private consolestream(inputstream in, string type) {         inputstream = in;         this.type = type;     }      public void run() {         try {             inputstreamreader = new inputstreamreader(inputstream);             bufferedreader br = new bufferedreader(is);             string read = null;             read = br.readline();             while(read != null) {                 controller.appendtext(read + "\n");                 read = br.readline();             }         } catch (ioexception e) {             e.printstacktrace();  //to change body of catch statement use file | settings | file templates.         }         controller.appendtext("thread" + type + "started");      }      private final inputstream inputstream;     private string type; }  private static console console = null; private consolecontroller controller; private stage stage; private printstream printstream; private pipedoutputstream custompipedoutputstream; private pipedoutputstream errorpipedoutputstream; private pipedoutputstream outpipedoutputstream; private pipedinputstream custompipedinputstream; private pipedinputstream errorpipedinputstream; private pipedinputstream outpipedinputstream; private thread customoutputthread; private thread outoutputthread; private thread erroroutputthread; } 

but result only: "start console", there no results of controller.appendtext("thread" + type + "started"); seems threads don't start. why?

i think have load form before can controller instance

fxmlloader loader = new fxmlloader(this.getclass().getresource("console.fxml"),resourcebundle); parent p = (parent) loader.load() controller = loader.getcontroller(); scene scene = new scene(p);