AndroidでRadioButtonを出す

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/activity_main"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context="com.example.joji.mytest2.MainActivity">

    <RadioGroup
        android:id="@+id/rgroup"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:orientation="vertical"
        >
    <RadioButton
        android:id="@+id/rg1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="windows"
        android:checked="true"
        />
    <RadioButton
        android:id="@+id/rg2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Linux"
        />
    <RadioButton
        android:id="@+id/rg3"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Mac"
        />
    </RadioGroup>

</RelativeLayout>

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.widget.CheckBox;
import android.widget.CompoundButton;
import android.widget.RadioButton;
import android.widget.RadioGroup;
import android.widget.Switch;
import android.widget.Toast;
import android.widget.ToggleButton;

public class MainActivity extends AppCompatActivity {

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

        RadioGroup rgroup = (RadioGroup)findViewById(R.id.rgroup);
        rgroup.setOnCheckedChangeListener(
            new RadioGroup.OnCheckedChangeListener(){
                public void onCheckedChanged(RadioGroup group, int checkedId){
                    RadioButton radio = (RadioButton)group.findViewById(checkedId);
                    Toast.makeText(
                            MainActivity.this,
                            String.format("[%s]が選択されました", radio.getText()),
                            Toast.LENGTH_SHORT).show();
                };
            }
        );
    }
}