public void getDataFromServer() {

    databaseReference.child("Katka List").addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            if(dataSnapshot.exists())
            {
                for(DataSnapshot postSnapShot:dataSnapshot.getChildren())
                {
                    KatkaInformation katka=postSnapShot.getValue(KatkaInformation.class);
                    TextView.setText //???
                    TextView.setText //???
                    TextView.setText //???
                    katkaListAdapter.notifyDataSetChanged();
                }
            }

        }
        @Override
        public void onCancelled(DatabaseError databaseError) {

        }
    });
}

private void CreateKatkaData(){
    if(validateForm())
    {
        String start=startView.getText().toString().trim();
        String finish=finishView.getText().toString().trim();
        String mdate=currentDateTime.getText().toString().trim();

        // create user object and set all the properties
        KatkaInformation katka = new KatkaInformation();
        katka.setPointStart(start);
        katka.setPointFinish(finish);
        katka.setDate(mdate);
        ;
        if(firebaseAuth.getCurrentUser()!=null)
        {
            // save the user at UserNode under user UID
            databaseReference.child("Katka List").child(firebaseAuth.getCurrentUser().getUid()).setValue(katka, new DatabaseReference.CompletionListener() {
                @Override
                public void onComplete(DatabaseError databaseError, DatabaseReference databaseReference) {
                    if(databaseError==null)
                    {
                        Toast.makeText(Main2Activity.this, "Data is saved successfully",
                                Toast.LENGTH_SHORT).show();
                        finish();

                        Intent intent = new Intent(Main2Activity.this, MainActivity.class);
                        startActivity(intent);

                    }
                }
            });

        }

    }
}