How to Make an Android Studio Calling App

XML (activity_main.xml)

<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:id="@+id/activity_main"
    android:orientation="vertical"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:gravity="center_horizontal|center_vertical"
    >

    <EditText
        android:id="@+id/et_phone_no"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_marginTop="80dp"
        android:hint="Enter Phone number"
        android:inputType="phone"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <Button
        android:id="@+id/btn_dial"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center_horizontal"
        android:layout_marginTop="80dp"
        android:text="Dial"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/et_phone_no" />


</android.support.constraint.ConstraintLayout>

 JAVA (MainActivity.java)

import android.content.Intent;
import android.net.Uri;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.text.TextUtils;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;

public class PhoneCallsactivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_phone_callsactivity);

        Button mDialButton = (Button) findViewById(R.id.btn_dial);
        final EditText mPhoneNoEt = (EditText) findViewById(R.id.et_phone_no);

        mDialButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                String phoneNo = mPhoneNoEt.getText().toString();
                if(!TextUtils.isEmpty(phoneNo)) {
                    String dial = "tel:" + phoneNo;
                    startActivity(new Intent(Intent.ACTION_DIAL, Uri.parse(dial)));
                }else {
                    Toast.makeText(PhoneCallsactivity.this, "Enter a phone number", Toast.LENGTH_SHORT).show();
                }
            }
        });
    }
}