RadioButton aplicacion Android

[ojimenezg2000]

-------.java--------
public class PagGramatica extends Activity implements RadioGroup.OnCheckedChangeListener,
View.OnClickListener{

protected static int respuesta = -1;
protected static int choice = -2;
private RadioGroup mRadioGroup;



public void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.tema1);
mRadioGroup.setOnCheckedChangeListener(this);
RadioButton r2 = (RadioButton) findViewById(R.id.option2);
Button ClearButton = (Button) findViewById(R.id.BtnLimpiar);
Button AnswerButton = (Button)findViewById(R.id.BtnAceptar);
respuesta = r2.getId();
ClearButton.setOnClickListener(this);
}
public void onCheckedChanged(RadioGroup group, int checkedId){
if (checkedId == R.id.option2){
ContadorAcierto++; }
}


public void onChechedChanged(RadioGroup arg0, int checkedId){
choice = checkedId;
}

public void onClick(View view){
mRadioGroup.clearCheck();
}
}

Os pongo elcodigo para a ver si me podeis echar una mano por favor