How to create a round/circle Button in Android

Hello, following their application guide for you.
The first step you create contain layout activity_demo

<?xml version="1.0" encoding="utf-8"?><LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"    android:orientation="vertical" android:layout_width="match_parent"    android:layout_height="match_parent">

    <Button        android:id ="@+id/btn_button"        android:layout_width="150dp"        android:layout_height="150dp"        android:layout_gravity="center_horizontal"        android:text="Round Button _Tienanh_it"        android:background="@drawable/button_bg_round_tienanhit"        android:padding="15dp"        />
</LinearLayout>

 Create backbgound button button_bg_round_tienanhit
  

<?xml version="1.0" encoding="utf-8"?><selector xmlns:android="http://schemas.android.com/apk/res/android">
    <item>
        <shape android:shape="oval">
            <stroke android:color="#1E90FF" android:width="5dp" />
            <solid android:color="#87CEEB"/>
            <size android:width="150dp" android:height="150dp"/>
        </shape>
    </item>
</selector>

The second step is to create class Demo1 extend Activity.

import com.anhttvn.democodeandroid.R;

/** * Created by Huu Duan on 10/26/2017. * @author anhtt */public class Demo1 extends Activity {
    @Override    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_demo1);
    }
}