android - Firebase - Check if data exist and add them -

i want check if user member of specific team, if user isn't ask join, if is, directed page. did find of similar question somehow still couldn't add user database. below code , code crash whenever click on 1 of list.

databasemembers = firebasedatabase.getinstance().getreference("members");  listviewteams.setonitemclicklistener(new adapterview.onitemclicklistener() {         @override         public void onitemclick(adapterview<?> adapterview, view view, int i, long l) {             //getting selected team             team team = teams.get(i);             checkmember();               //creating intent             intent intent = new intent(getapplicationcontext(), chatroomactivity.class);              //putting team name , id intent             intent.putextra(team_id, team.getteamid());             intent.putextra(team_name, team.getteamname());              //starting activity intent             startactivity(intent);         }     });  private void checkmember(){     firebaseuser user = firebaseauth.getcurrentuser();     final string teammember = user.getemail();     databasemembers.addlistenerforsinglevalueevent(new valueeventlistener() {         @override         public void ondatachange(datasnapshot datasnapshot) {             if(datasnapshot.haschild(teammember)){                 finish();             }             else{                 databasemembers.push().setvalue(teammember);             }         }          @override         public void oncancelled(databaseerror databaseerror) {          }     }); } 

logcat:

04-07 12:44:41.167 19091-19091/com.example.user.stfv2 e/androidruntime: fatal exception: main                                                                     process: com.example.user.stfv2, pid: 19091                                                                     com.google.firebase.database.databaseexception: invalid firebase database path: haha@gmail.com. firebase database paths must not contain '.', '#', '$', '[', or ']'                                                                         @ com.google.android.gms.internal.zzbtf.zzjl(unknown source)                                                                         @ com.google.firebase.database.datasnapshot.haschild(unknown source)                                                                         @ com.example.user.stfv2.mainactivity$8.ondatachange(mainactivity.java:352)                                                                         @ com.google.firebase.database.query$1.ondatachange(unknown source)                                                                         @ com.google.android.gms.internal.zzbpx.zza(unknown source)                                                                         @ com.google.android.gms.internal.zzbqx.zzzs(unknown source)                                                                         @ com.google.android.gms.internal.zzbra$1.run(unknown source)                                                                         @ android.os.handler.handlecallback(handler.java:739)                                                                         @ android.os.handler.dispatchmessage(handler.java:95)                                                                         @ android.os.looper.loop(looper.java:148)                                                                         @ android.app.activitythread.main(activitythread.java:5417)                                                                         @ java.lang.reflect.method.invoke(native method)                                                                         @ com.android.internal.os.zygoteinit$methodandargscaller.run(zygoteinit.java:726)                                                                         @ com.android.internal.os.zygoteinit.main(zygoteinit.java:616) 

my database:

when user click on "heng" team, check if user's email exist in database, if isn't add user's email teammember. can add user created team, can't seem add users wants join later. appreciate if me. let me know if there's lack of information.

the problem firebase not accept . (dot) symbol in key. in order use email address, need have encoding method. email addres must name@mail,com (see , comma) in stead of nume@email.com in case. these methods encode , decode email address.

static string encodeuseremail(string useremail) {     return useremail.replace(".", ","); } static string decodeuseremail(string useremail) {     return useremail.replace(",", "."); } 

this methods solve problem.