Android LinearLayout weight_sum and weight properties

<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"
    tools:context="com.blogspot.shalvinpd.linearlayouteg.MainActivity"
    android:weightSum="2">

    <TextView
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:gravity="center"
        android:layout_weight="1"
        android:text="Hello World!"
        android:background="@color/colorPrimary"/>

    <TextView
        android:layout_width="match_parent"
        android:background="@color/colorAccent"
        android:layout_height="wrap_content"
        android:layout_weight="1"
        android:text="Hello World!" />
</LinearLayout>