Radio Group Android Studio

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="jovial.etutorialscafe.radiobutton.MainActivity">

    <TextView
        android:gravity="center"
        android:text="Rate the Application"
        android:layout_width="368dp"
        android:layout_height="0dp"
        android:layout_marginBottom="8dp"
        app:layout_constraintBottom_toTopOf="@+id/radioGroup"
        android:layout_marginLeft="8dp"
        app:layout_constraintLeft_toLeftOf="parent"
        android:layout_marginRight="8dp"
        app:layout_constraintRight_toRightOf="parent"
        android:layout_marginStart="8dp"
        android:layout_marginEnd="8dp" />
    <RadioGroup
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        android:id="@+id/radioGroup">

        <RadioButton
            android:id="@+id/excelentID"
            android:text="Excelent"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content" />

        <RadioButton
            android:id="@+id/goodID"
            android:text="Good"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content" />
        <RadioButton
            android:id="@+id/avdID"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="Average"/>

        <RadioButton
            android:id="@+id/poorID"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="Poor" />


    </RadioGroup>

    <Button
        android:id="@+id/buttonID"
        android:text="Sumbit rate"
        android:layout_width="wrap_content"
        android:layout_height="48dp"
        android:layout_marginTop="8dp"
        app:layout_constraintTop_toBottomOf="@+id/radioGroup"
        android:layout_marginLeft="8dp"
        app:layout_constraintLeft_toLeftOf="parent"
        android:layout_marginRight="8dp"
        app:layout_constraintRight_toRightOf="parent" />

</android.support.constraint.ConstraintLayout>

RadioGroupMainActivity.java

package jovial.etutorialscafe.radiobutton;

import android.support.annotation.IdRes;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.RadioButton;
import android.widget.RadioGroup;
import android.widget.Toast;

public class MainActivity extends AppCompatActivity {

    RadioGroup rate;
    RadioButton exce,good,avg,poor;
    String ratecomment = "";
    Button buttonSumbit;

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

        rate = (RadioGroup)findViewById(R.id.radioGroup);

        exce = (RadioButton)findViewById(R.id.excelentID);
        good = (RadioButton)findViewById(R.id.goodID);
        avg = (RadioButton)findViewById(R.id.avdID);
        poor = (RadioButton)findViewById(R.id.poorID);

        buttonSumbit = (Button)findViewById(R.id.buttonID);

        rate.setOnCheckedChangeListener(new RadioGroup.OnCheckedChangeListener() {
            @Override
            public void onCheckedChanged(RadioGroup group, @IdRes int checkedId) {

                switch (rate.indexOfChild(findViewById(group.getCheckedRadioButtonId()))){
                    case 0:
                        ratecomment = "Excellent";
                        break;
                    case 1:
                        ratecomment = "Good";
                        break;
                    case 2:
                        ratecomment = "Average";
                        break;
                    case 3:
                        ratecomment = "Poor";
                        break;
                }
            }
        });

        buttonSumbit.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Toast.makeText(MainActivity.this, ratecomment + " : Ratting Submited", Toast.LENGTH_SHORT).show();
            }
        });

    }
}