android - com.google.firebase.database.DatabaseException: Can't convert object of type java.lang.String -

i student studying android self. first question. please me.

09-12 01:35:35.723 2355-2355/com.example.jan.sanhakproject e/androidruntime:  fatal exception: main                                                                                  process: com.example.jan.sanhakproject, pid: 2355                                                                                  com.google.firebase.database.databaseexception: can't convert object of type java.lang.string type com.example.jan.sanhakproject.chat                                                                                      @ com.google.android.gms.internal.zzbqi.zze(unknown source)                                                                                      @ com.google.android.gms.internal.zzbqi.zzb(unknown source)                                                                                      @ com.google.android.gms.internal.zzbqi.zza(unknown source)                                                                                      @ com.google.firebase.database.datasnapshot.getvalue(unknown source)                                                                                      @ com.example.jan.sanhakproject.chatactivity$2.onchildadded(chatactivity.java:115)                                                                                      @ com.google.android.gms.internal.zzblz.zza(unknown source)                                                                                      @ com.google.android.gms.internal.zzbnz.zzyj(unknown source)                                                                                      @ com.google.android.gms.internal.zzboc$1.run(unknown source)                                                                                      @ android.os.handler.handlecallback(handler.java:751)                                                                                      @ android.os.handler.dispatchmessage(handler.java:95)                                                                                      @ android.os.looper.loop(looper.java:154)                                                                                      @ android.app.activitythread.main(activitythread.java:6077)                                                                                      @ java.lang.reflect.method.invoke(native method)                                                                                      @ com.android.internal.os.zygoteinit$methodandargscaller.run(zygoteinit.java:866)                                                                                      @ com.android.internal.os.zygoteinit.main(zygoteinit.java:756)     09-12 01:35:44.318 2355-2374/com.example.jan.sanhakproject w/dynamitemodule: local module descriptor class com.google.firebase.auth not found. 

chat.java

public class chat {

    public string email;      public string text;      public chat() {         // default constructor required calls datasnapshot.getvalue(comment.class)     }      public chat(string text) {          this.text = text;     }      public string getemail() {         return email;     }      public void setemail(string email) {         this.email = email;     }      public string gettext() {         return text;     }      public void settext(string text) {         this.text = text;     } } 

chatactivity.java

    public class chatactivity extends appcompatactivity {     string tag = this.getclass().getsimplename();     private databasereference mdatabase;     private firebasedatabase firebasedatabase;     private recyclerview mrecyclerview;     private recyclerview.adapter madapter;     private recyclerview.layoutmanager mlayoutmanager;     string[] mydataset = {"안녕", "오늘","뭐했어","영화볼래?"};     databasereference databasereference;       edittext ettext;     button btnsend;     string email;     list<chat> mchat;     firebasedatabase database;      @override     protected void oncreate(bundle savedinstancestate) {         super.oncreate(savedinstancestate);         setcontentview(r.layout.activity_chat);         firebasedatabase = firebasedatabase.getinstance();         databasereference = firebasedatabase.getreference();          //database = firebasedatabase.getinstance();         firebaseuser user = firebaseauth.getinstance().getcurrentuser();          if (user != null) {             // name, email address, , profile photo url             email = user.getemail();         }          intent in = getintent();         final string stchatid = in.getstringextra("frienduid");          ettext = (edittext) findviewbyid(r.id.ettext);         btnsend = (button) findviewbyid(r.id.btnsend);         btnsend.setonclicklistener(new view.onclicklistener() {             @override             public void onclick(view view) {                  string sttext = ettext.gettext().tostring();                  if (sttext.equals("") || sttext.isempty()) {                     toast.maketext(chatactivity.this, "내용을 입력해 주세요.", toast.length_short).show();                 } else {                     toast.maketext(chatactivity.this, email + "," + sttext, toast.length_short).show();                       calendar c = calendar.getinstance();                     simpledateformat df = new simpledateformat("yyyy-mm-dd hh:mm:ss");                     string formatteddate = df.format(c.gettime());                       databasereference = database.getreference("users").child(stchatid).child(formatteddate);                      hashtable<string, string> chat = new hashtable<string, string>();                     chat.put("email", email);                     chat.put("text", sttext);                     databasereference.setvalue(chat);                     ettext.settext("");                   }               }         });           mrecyclerview = (recyclerview) findviewbyid(r.id.my_recycler_view);          // use setting improve performance if know changes         // in content not change layout size of recyclerview         mrecyclerview.sethasfixedsize(true);          // use linear layout manager         mlayoutmanager = new linearlayoutmanager(this);         mrecyclerview.setlayoutmanager(mlayoutmanager);         mchat = new arraylist<>();         // specify adapter (see next example)         madapter = new myadapter(mchat, email, chatactivity.this);         mrecyclerview.setadapter(madapter);           databasereference.child("users").child(stchatid).child("chats").addchildeventlistener(new childeventlistener() {             @override             public void onchildadded(datasnapshot datasnapshot, string s) {                 chat chat = datasnapshot.getvalue(chat.class);                 mchat.add(chat);                   mrecyclerview.scrolltoposition(mchat.size() - 1);                 madapter.notifyiteminserted(mchat.size() - 1);             }              @override             public void onchildchanged(datasnapshot datasnapshot, string s) {              }              @override             public void onchildremoved(datasnapshot datasnapshot) {              }              @override             public void onchildmoved(datasnapshot datasnapshot, string s) {              }              @override             public void oncancelled(databaseerror databaseerror) {              }         });     }  } 

myadapter.java

public class myadapter extends recyclerview.adapter<myadapter.viewholder> {     private string[] mdataset;     list<chat> mchat;     string stemail;     context context;      // provide reference views each data item     // complex data items may need more 1 view per item, ,     // provide access views data item in view holder public static class viewholder extends recyclerview.viewholder {         // each data item string in case         public textview mtextview;          public viewholder(view itemview) {             super(itemview);             mtextview = (textview) itemview.findviewbyid(r.id.mtextview);         }     }      // provide suitable constructor (depends on kind of dataset)     public myadapter(list<chat> mchat, string email, context context) {         this.mchat = mchat;         this.stemail = email;         this.context = context;      }      @override     public int getitemviewtype(int position) {          if (mchat.get(position).getemail().equals(stemail)){             return 1;         } else {             return 2;         }     }      // create new views (invoked layout manager)     @override     public viewholder oncreateviewholder(viewgroup parent,                                                    int viewtype) {         // create new view         view v;         if (viewtype == 1) {             v = layoutinflater.from(parent.getcontext())                     .inflate(r.layout.right_text_view, parent, false);         } else {              v = layoutinflater.from(parent.getcontext())                     .inflate(r.layout.my_text_view, parent, false);         }         // set view's size, margins, paddings , layout parameters         viewholder vh = new viewholder(v);         return vh;     }      // replace contents of view (invoked layout manager)     @override     public void onbindviewholder(viewholder holder, final int position) {         // - element dataset @ position         // - replace contents of view element         holder.mtextview.settext(mchat.get(position).gettext());         holder.mtextview.setonclicklistener(new view.onclicklistener() {             @override             public void onclick(view view) {                 toast.maketext(context, string.valueof(position), toast.length_short).show();             }         });      }      // return size of dataset (invoked layout manager)     @override     public int getitemcount() {         return mchat.size();     } } 

the exception log indicates code trying value of object chat , finding string. error occurs @ statement in onchildadded():

chat chat = datasnapshot.getvalue(chat.class); 

check database confirm children of /users/stchatid/chats valid chat objects. looks listening new chats at: /users/stchatid/chats:

databasereference.child("users").child(stchatid).child("chats").addchildeventlistener(...) 

but writing chats @ location:

databasereference = database.getreference("users").child(stchatid).child(formatteddate);