Android 프로그램 개발 중 단일 선택 단추(RadioGroup)사용 에 대한 자세 한 설명

<LinearLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools" 
android:layout_width="match_parent" 
android:layout_height="match_parent" 
tools:context=".MainActivity" 
android:orientation="vertical"> 
<TextView 
android:id="@+id/txt" 
android:layout_width="fill_parent" 
android:layout_height="wrap_content" 
android:text="     "/> 
<RadioGroup 
android:id="@+id/sex" 
android:layout_width="fill_parent" 
android:layout_height="wrap_content"> 
<RadioButton 
android:id="@+id/male" 
android:text=" "/> 
<RadioButton 
android:id="@+id/female" 
android:text=" "/> 
</RadioGroup> 
</LinearLayout> 

public class
MainActivity extends Activity { 
private TextView txt=null; 
private RadioGroup sex=null; 
private RadioButton male=null; 
private RadioButton female=null; 
@Override 
protected void
onCreate(Bundle savedInstanceState) { 
super.onCreate(savedInstanceState); 
setContentView(R.layout.activity_main); 
this.txt=(TextView)
super.findViewById(R.id.txt); 
this.sex=(RadioGroup)
super.findViewById(R.id.sex); 
this.male=(RadioButton)
super.findViewById(R.id.male); 
this.female=(RadioButton)
super.findViewById(R.id.female); 
this.sex.setOnCheckedChangeListener(new
OnCheckedChangeListenerImp()); 
} private class
OnCheckedChangeListenerImp implements
OnCheckedChangeListener{ 
public void
onCheckedChanged(RadioGroup group, int checkedId)
{ String temp=null; 
if(MainActivity.this.male.getId()==checkedId){ 
temp=" "; 
} else if(MainActivity.this.female.getId()==checkedId){ 
temp=" "; 
} MainActivity.this.txt.setText("     "+temp); 
} }