Berikut adalah code untuk melakukan input data ke Firebase

activity_write_data_firebase.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="#bb013d60"
    android:padding="16dp"
    android:gravity="center">
    <TextView
        android:id="@+id/title"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Simple Firebase"
        android:padding="10dp"
        android:textSize="34sp"
        android:textColor="#fff"
        android:textStyle="bold|italic"
        android:layout_marginBottom="20dp"
        android:layout_centerHorizontal="true"/>
    <EditText
        android:id="@+id/textTitle"
        android:layout_below="@id/title"
        android:background="#fff"
        android:padding="10dp"
        android:layout_width="match_parent"
        android:layout_height="wrap_content" />


    <EditText
        android:id="@+id/textInput"
        android:layout_below="@id/textTitle"
        android:layout_marginTop="20dp"
        android:background="#fff"
        android:padding="10dp"
        android:layout_width="match_parent"
        android:layout_height="wrap_content" />
    <Button
        android:layout_below="@id/textInput"
        android:id="@+id/btnSubmit"
        android:background="#dc304a9f"
        android:textColor="#fff"
        android:layout_marginRight="70dp"
        android:layout_marginLeft="70dp"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_marginTop="24dp"
        android:text="Submit"/>
</RelativeLayout>

WriteFirebaseActivity.java

public class WriteFirebaseActivity extends AppCompatActivity {

    Activity activity;
    EditText textTitle, textInput;
    Button submit;
    DatabaseReference rootRef, demoRef;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_write_data_firebase);
        activity = this;

        textTitle = (EditText) findViewById(R.id.textTitle);
        textInput = (EditText) findViewById(R.id.textInput);
        submit = (Button) findViewById(R.id.btnSubmit);


        rootRef = FirebaseDatabase.getInstance().getReference();
        submit.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                String strTextTitle = textTitle.getText().toString();
                String strtextInput = textInput.getText().toString();
                demoRef = rootRef.child("demo").push();
                demoRef.child("textTitle").setValue(strTextTitle);
                demoRef.child("textInput").setValue(strtextInput);
                demoRef.child("date").setValue(getDateTime());

                startActivity(new Intent(activity, GetFirebaseActivity.class));
            }
        });
    }

    @Override
    protected void onResume() {
        super.onResume();
        ResetField();
    }

    public void ResetField() {
        textTitle.setText("");
        textInput.setText("");
    }

    private String getDateTime() {
        DateFormat dateFormat = new SimpleDateFormat("yyyy/MM/dd HH:mm:ss");
        Date date = new Date();
        return dateFormat.format(date);
    }
}