gistfile1.java

package com.button.radio;

import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.RadioButton;
import android.widget.RadioGroup;
import android.widget.Toast;

public class Selector extends Activity {

    private RadioGroup radioGroup;
    private RadioButton radioSexButton;
    private Button btnDisplay;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

        radioGroup = (RadioGroup) findViewById(R.id.radioGroup);
        btnDisplay = (Button) findViewById(R.id.btnDisplay);

        btnDisplay.setOnClickListener(new OnClickListener() {

            @Override
            public void onClick(View v) {
                // THESE ARE THE MOST IMPORTANT LINES
                int selectedId = radioGroup.getCheckedRadioButtonId();
                radioSexButton = (RadioButton) findViewById(selectedId);
                // END MOST IMPORTANT LINES

                Toast.makeText(Selector.this, radioSexButton.getText(), Toast.LENGTH_SHORT).show();
            }
        });
    }
}


<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    >
<TextView  
    android:layout_width="fill_parent" 
    android:layout_height="wrap_content" 
    android:text="@string/hello"
    />
    
    <RadioGroup
        android:id="@+id/radioGroup"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" >
 
        <RadioButton
            android:id="@+id/radioMale"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="@string/radio_male" 
            android:checked="true" />
 
        <RadioButton
            android:id="@+id/radioFemale"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="@string/radio_female" />
            
        <RadioButton
            android:id="@+id/radioFemale"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="@string/radio_forget" />
    </RadioGroup>
    <Button
        android:id="@+id/btnDisplay"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/btn_display" />
        
</LinearLayout>

Feel free to use radioGroup.setOnCheckedChangeListener(new RadioGroup.OnCheckedChangeListener() { }); instead of the button and its listener.