mchat | Simple chat system that can do file transfers | Websocket library

public class MessageActivity extends AppCompatActivity {

    TextView username;
    ImageView imageView;
    RecyclerView recyclerViewy;
    EditText msg_editText;
    ImageButton sendBtn;


    FirebaseUser fuser;
    DatabaseReference references;
    Intent intent;

    MessageAdapter messageAdapter;
    Listmchat;
    RecyclerView recyclerView;


    @Override
     protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_message);

        imageView = findViewById(R.id.imageview_profile);
        username = findViewById(R.id.usernamey);
        sendBtn = findViewById(R.id.btn_send);
        msg_editText = findViewById(R.id.text_send);
        recyclerView = findViewById(R.id.recycler_view);




        recyclerView.setHasFixedSize(true);


        LinearLayoutManager linearLayoutManager = new LinearLayoutManager(getApplicationContext());
        linearLayoutManager.setStackFromEnd(true);
        recyclerView.setLayoutManager(linearLayoutManager);


        intent = getIntent();
        String userid = intent.getStringExtra("userid");

        fuser = FirebaseAuth.getInstance().getCurrentUser();
        references = FirebaseDatabase.getInstance().getReference("MyUsers").child(userid);

        references.addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(@NonNull DataSnapshot snapshot) {
                Users users = snapshot.getValue(Users.class);
                username.setText(users.getUsername());

                if (users.getImageURL().equals("default")){
                    imageView.setImageResource(R.mipmap.ic_launcher);

                }else {
                    Glide.with(MessageActivity.this)
                            .load(users.getImageURL())
                            .into(imageView);
                }


                readMessages(fuser.getUid(),userid,users.getImageURL());

            }

            @Override
            public void onCancelled(@NonNull DatabaseError error) {

            }
        });

        sendBtn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                String msg = msg_editText.getText().toString();

                if (!msg .equals("")){
                    sendMessage(fuser.getUid(),userid,msg);
                }else {
                    Toast.makeText(MessageActivity.this, "please send a non empty message !", Toast.LENGTH_SHORT).show();
                }
                msg_editText.setText("");


            }
        });




    }

     private void sendMessage(String sender,String receiver ,String message){
        DatabaseReference reference = FirebaseDatabase.getInstance().getReference();

        HashMap hashMap =new HashMap<>();
        hashMap.put("sender",sender);
        hashMap.put("receiver",receiver);
        hashMap.put("message",message);

        reference.child("Chats").push().setValue(hashMap);
    }


     private void readMessages(String myid,String userid,String imgurl){
       mchat = new ArrayList<>();
       references = FirebaseDatabase.getInstance().getReference("Chats");

       references.addValueEventListener(new ValueEventListener() {
           @Override
           public void onDataChange(@NonNull DataSnapshot snapshot) {
               mchat.clear();
               for (DataSnapshot dataSnapshot :snapshot.getChildren()){

                   Chat chat = dataSnapshot.getValue(Chat.class);

                   if (chat.getReceiver().equals(myid)&&chat.getSender().equals(userid)&&chat.getReceiver().equals(userid)&&chat.getSender().equals(myid)){
                       mchat.add(chat);
                   }
                   messageAdapter = new MessageAdapter(MessageActivity.this,mchat,imgurl);
                   recyclerView.setAdapter(messageAdapter);
               }

           }

           @Override
           public void onCancelled(@NonNull DatabaseError error) {

           }
       });


    }
   }