Posting the error message would certainly make it easier to help you with the problem. Is it a run-time error or IDE error?
		
		
	 
Thanks for your suggestion.
here is the error log:
Waiting for debugger to connect...
Program started.
Error occurred on line: 20 (Main)
java.lang.RuntimeException: Field: config not found in: flm.b4j.mqttbroker.MQTTBrokerExtended
    at anywheresoftware.b4j.object.JavaObject$FieldCache.getField(JavaObject.java:307)
    at anywheresoftware.b4j.object.JavaObject.GetField(JavaObject.java:182)
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.base/java.lang.reflect.Method.invoke(Method.java:564)
    at anywheresoftware.b4a.shell.Shell.runMethod(Shell.java:629)
    at anywheresoftware.b4a.shell.Shell.raiseEventImpl(Shell.java:234)
    at anywheresoftware.b4a.shell.Shell.raiseEvent(Shell.java:167)
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.base/java.lang.reflect.Method.invoke(Method.java:564)
    at anywheresoftware.b4a.BA.raiseEvent2(BA.java:111)
    at anywheresoftware.b4a.shell.ShellBA.raiseEvent2(ShellBA.java:100)
    at anywheresoftware.b4a.BA.raiseEvent(BA.java:98)
    at b4j.example.main.main(main.java:29)
I post the code.please have a look. Thanks for your help.