activity_main.xml

<LinearLayout 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"
    android:orientation="vertical"
    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.google.firebase.quickstart.fcm.java.MainActivity">

    <ImageView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginBottom="16dp"
        android:layout_gravity="center_horizontal"
        android:src="@drawable/firebase_lockup_400" />

    <TextView
        android:id="@+id/informationTextView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center_horizontal"
        android:gravity="center_horizontal"
        android:text="@string/quickstart_message" />

    <Button
        android:id="@+id/subscribeButton"
        android:layout_width="@dimen/standard_field_width"
        android:layout_height="wrap_content"
        android:layout_gravity="center_horizontal"
        android:layout_marginTop="20dp"
        android:text="@string/subscribe_to_weather" />

    <Button
        android:id="@+id/logRegistrationButton"
        android:layout_width="@dimen/standard_field_width"
        android:layout_height="wrap_content"
        android:layout_gravity="center_horizontal"
        android:text="@string/log_token" />

</LinearLayout>