Cara Menggunakan RadioButton di Android

<RadioGroup
    android:id="@+id/radio"
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"
    android:orientation="horizontal">


    <RadioButton android:id="@+id/radPa"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Laki-laki"
        android:checked="true" />

    <RadioButton android:id="@+id/radPi"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Perempuan" />
</RadioGroup>

//deklarasi variabel
RadioGroup rg;
String JK;
RadioButton radPa , radPi;

//====================================================

//inisialisasi view(void onCreate())
radPa=(RadioButton) findViewById(R.id.radPa);
radPi=(RadioButton) findViewById(R.id.radPi);
rg = (RadioGroup) findViewById(R.id.radio);

//====================================================
//get value
if(JK.equalsIgnoreCase("Perempuan")){
 ((RadioButton)rg.getChildAt(1)).setChecked(true);
}else{//Laki-laki
 ((RadioButton)rg.getChildAt(0)).setChecked(true);
}


//====================================================

// set value
String ljenis_kelamin="Perempuan";
if(radPa.isChecked()){
ljenis_kelamin="Laki-Laki";
}