activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <EditText
        android:id="@+id/editText1"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_marginLeft="16dp"
        android:layout_marginStart="16dp"
        android:layout_marginTop="16dp"
        android:ems="10"
        android:hint="@string/edit_message1"
        android:inputType="textPersonName"
        app:layout_constraintEnd_toStartOf="@+id/button"
        app:layout_constraintHorizontal_bias="0.5"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <Button
        android:id="@+id/button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginEnd="16dp"
        android:layout_marginLeft="16dp"
        android:layout_marginRight="16dp"
        android:layout_marginStart="16dp"
        android:onClick="sendMessage"
        android:text="@string/button_send"
        app:layout_constraintBaseline_toBaselineOf="@+id/editText1"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toEndOf="@+id/editText1" />

    <EditText
        android:id="@+id/editText2"
        android:layout_width="0dp"
        android:layout_height="45dp"
        android:layout_marginEnd="8dp"
        android:layout_marginLeft="16dp"
        android:layout_marginRight="8dp"
        android:layout_marginStart="16dp"
        android:layout_marginTop="16dp"
        android:ems="10"
        android:hint="@string/edit_message2"
        android:inputType="textPersonName"
        app:layout_constraintEnd_toStartOf="@+id/button"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/editText1" />

    <EditText
        android:id="@+id/editText3"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_marginStart="16dp"
        android:layout_marginLeft="16dp"
        android:layout_marginTop="72dp"
        android:layout_marginEnd="8dp"
        android:layout_marginRight="8dp"
        android:ems="10"
        android:hint="@string/search_text"
        android:inputType="textPersonName"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.0"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/editText2" />

    <Button
        android:id="@+id/button2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="8dp"
        android:layout_marginEnd="64dp"
        android:layout_marginRight="64dp"
        android:layout_marginBottom="8dp"
        android:onClick="searchBooks"
        android:text="Search"
        app:layout_constraintBottom_toTopOf="@+id/textView2"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/editText3" />

    <TextView
        android:id="@+id/textView2"
        android:layout_width="0dp"
        android:layout_height="131dp"
        android:layout_marginStart="16dp"
        android:layout_marginLeft="16dp"
        android:layout_marginTop="76dp"
        android:layout_marginEnd="8dp"
        android:layout_marginRight="8dp"
        android:background="@drawable/my_border"
        android:fadingEdge="horizontal"
        android:text="Search Results"
        android:textSize="15sp"
        android:textStyle="bold"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.0"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/editText3" />

    <RadioGroup xmlns:android="http://schemas.android.com/apk/res/android"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="8dp"
        android:layout_marginLeft="8dp"
        android:layout_marginTop="32dp"
        android:layout_marginEnd="8dp"
        android:layout_marginRight="8dp"
        android:checkedButton="@+id/radio_title"
        android:orientation="horizontal"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/textView2">


        <RadioButton
            android:id="@+id/radio_title"
            android:layout_width="76dp"
            android:layout_height="wrap_content"
            android:onClick="onRadioButtonClicked"
            android:text="@string/search_title" />

        <RadioButton
            android:id="@+id/radio_author"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:onClick="onRadioButtonClicked"
            android:text="@string/search_author" />
    </RadioGroup>

</android.support.constraint.ConstraintLayout>