How to create Radio Buttons in Android studio - Java

MainActivity.java

package com.example.youtuberadio;

import androidx.appcompat.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.TextView;
import android.widget.Toast;

public class MainActivity extends AppCompatActivity {
RadioButton radioButton;
RadioGroup radioGroup;
TextView textView;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        radioGroup=findViewById(R.id.rGroup);
        textView=findViewById(R.id.view_selected);

        //variable for the button
       Button buttonOk =findViewById(R.id.btn_ok);
       buttonOk.setOnClickListener(new View.OnClickListener() {
           @Override
           public void onClick(View v) {
               int radioId=radioGroup.getCheckedRadioButtonId();
               radioButton=findViewById(radioId);

               textView.setText("You selected: "+radioButton.getText());
           }
       });
    }

    public void checkOk(View v){
        int radioId=radioGroup.getCheckedRadioButtonId();
        radioButton=findViewById(radioId);

        Toast.makeText(this,"You have clicked on: "+ radioButton.getText(),Toast.LENGTH_SHORT).show();
    }
}

Activity_Main.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout 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">
<RadioGroup
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:id="@+id/rGroup"
    android:layout_centerInParent="true">
    <RadioButton
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/male"
        android:text="Male"
        android:onClick="checkOk"/>
    <RadioButton
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/female"
        android:text="Female"
        android:onClick="checkOk"/>
    <RadioButton
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/other"
        android:text="Other"
        android:onClick="checkOk"/>
    <RadioButton
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/rather"
        android:text="Rather Not Say"
        android:onClick="checkOk"
        android:checked="true"/>
</RadioGroup>

    <TextView
        android:id="@+id/view_selected"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_below="@+id/rGroup"
        android:layout_marginStart="141dp"
        android:layout_marginLeft="141dp"
        android:layout_marginTop="-4dp"
        android:text="Your choice"
        android:textSize="20sp" />

    <Button
        android:id="@+id/btn_ok"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_below="@+id/view_selected"
        android:layout_marginStart="145dp"
        android:layout_marginLeft="145dp"
        android:layout_marginTop="0dp"
        android:text="OK" />
</RelativeLayout>