Fragments goes one behind the other

i made a 2 fragment layout one for the login screen and the other for the Register screen and in the main screen i put a fragment for login screen and a button if the user want to register he click in that button and the register fragment appears to him and the login fragment disappear the problem is after i press the register button in the main screen the login screen appears to be behind the register screen here's a photo for it login behind Register i don't know what's the problem or i misunderstanding the fragments i don't know here's the onclick method on the MainActity class

  @Override
                        public void onClick(View view) {
                            String mytxt = inversebutton.getText().toString();
                            Fragment fragmentSign = new Signin();
                            Fragment fragmentregister = new Register();
                            if(mytxt.equals("Register")){  // call signin frame
                                android.support.v4.app.FragmentManager fragmentManager= getSupportFragmentManager();
                                fragmentManager.beginTransaction().replace(R.id.fragmentplace ,fragmentregister).commit();
                                inversebutton.setText("SignIn");
                            }else{ // call register fra
                                android.support.v4.app.FragmentManager fragmentManager= getSupportFragmentManager();
                                fragmentManager.beginTransaction().replace(R.id.fragmentplace ,fragmentSign).commit();
                                inversebutton.setText("Register");
                            }
                        }
                    });

here's the activitymain.xml

 <?xml version="1.0" encoding="utf-8"?>
    <RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
        xmlns:tools="http://schemas.android.com/tools"
        android:id="@+id/activity_main"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:paddingBottom="@dimen/activity_vertical_margin"
        android:paddingLeft="@dimen/activity_horizontal_margin"
        android:paddingRight="@dimen/activity_horizontal_margin"
        android:paddingTop="@dimen/activity_vertical_margin"
        tools:context="com.example.abdelmagied.myapplication.MainActivity"
        android:background="#222">

        <fragment
            android:layout_width="match_parent"
            android:layout_height="300dp"
            android:name="com.example.abdelmagied.myapplication.Signin"
            android:id="@+id/fragmentplace"
            android:layout_centerVertical="true"
            android:layout_alignParentLeft="true"
            android:layout_alignParentStart="true" />

        <Button
            android:text="Register"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:id="@+id/reverse"
            android:layout_alignParentTop="true"
            android:layout_alignParentRight="true"
            android:layout_alignParentEnd="true"
            android:layout_marginTop="16dp" />

    </RelativeLayout>

here's the register_fragment class

  public class Register extends Fragment {
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    // Inflate the layout for this fragment
    return inflater.inflate(R.layout.fragment_register, container, false);
}

here's the signin fragment class

public class Register extends Fragment {
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    // Inflate the layout for this fragment
    return inflater.inflate(R.layout.fragment_register, container, false);
}

here's the fragment_register.xml

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
        xmlns:tools="http://schemas.android.com/tools"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        tools:context="com.example.abdelmagied.myapplication.Register"
        android:background="#090"
        android:id="@+id/registerfragment">

        <!-- TODO: Update blank fragment layout -->

        <TextView
            android:text="Name"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_alignParentTop="true"
            android:layout_alignParentLeft="true"
            android:layout_alignParentStart="true"
            android:layout_marginLeft="32dp"
            android:layout_marginStart="32dp"
            android:layout_marginTop="49dp"
            android:id="@+id/textView" />

        <TextView
            android:text="Password"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_below="@+id/textView"
            android:layout_alignLeft="@+id/textView"
            android:layout_alignStart="@+id/textView"
            android:layout_marginTop="61dp"
            android:id="@+id/textView3" />

        <EditText
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:inputType="textPersonName"
            android:ems="10"
            android:layout_alignParentTop="true"
            android:layout_alignLeft="@+id/Rbutton"
            android:layout_alignStart="@+id/Rbutton"
            android:layout_marginTop="30dp"
            android:id="@+id/registerN" />

        <EditText
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:inputType="textPassword"
            android:ems="10"
            android:layout_below="@+id/registerN"
            android:layout_alignRight="@+id/registerN"
            android:layout_alignEnd="@+id/registerN"
            android:layout_marginTop="36dp"
            android:id="@+id/Rpassword" />

        <EditText
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:inputType="textPassword"
            android:ems="10"
            android:id="@+id/RRpassword"
            android:layout_alignBaseline="@+id/textView4"
            android:layout_alignBottom="@+id/textView4"
            android:layout_alignLeft="@+id/Rbutton"
            android:layout_alignStart="@+id/Rbutton" />

        <Button
            android:text="Register"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:id="@+id/Rbutton"
            android:layout_below="@+id/textView4"
            android:layout_centerHorizontal="true"
            android:layout_marginTop="57dp" />

        <TextView
            android:text="Rpassword"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:id="@+id/textView4"
            android:layout_centerVertical="true"
            android:layout_alignLeft="@+id/textView3"
            android:layout_alignStart="@+id/textView3" />
    </RelativeLayout>

here's the fragment_signin.xml

    <RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
        xmlns:tools="http://schemas.android.com/tools"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        tools:context="com.example.abdelmagied.myapplication.Signin"
        android:background="#878"
        android:id="@+id/signinfragment">

        <!-- TODO: Update blank fragment layout -->

        <TextView
            android:text="Name"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_marginLeft="55dp"
            android:layout_marginStart="55dp"
            android:id="@+id/sn"
            android:layout_alignParentTop="true"
            android:layout_alignParentLeft="true"
            android:layout_alignParentStart="true"
            android:layout_marginTop="46dp" />

        <TextView
            android:text="Password"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_below="@+id/sn"
            android:layout_alignLeft="@+id/sn"
            android:layout_alignStart="@+id/sn"
            android:layout_marginTop="79dp"
            android:id="@+id/textView2" />

        <EditText
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:inputType="textPersonName"
            android:ems="10"
            android:layout_above="@+id/textView2"
            android:layout_alignParentRight="true"
            android:layout_alignParentEnd="true"
            android:id="@+id/sname" />

        <EditText
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:inputType="textPassword"
            android:ems="10"
            android:layout_alignBottom="@+id/textView2"
            android:layout_alignLeft="@+id/sname"
            android:layout_alignStart="@+id/sname"
            android:id="@+id/signpassword" />

        <Button
            android:text="SignIn"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:id="@+id/Sbuton"
            android:layout_below="@+id/signpassword"
            android:layout_centerHorizontal="true"
            android:layout_marginTop="51dp" />
    </RelativeLayout>