我想通過按鈕來觸發再來一局，但是沒有用，

start函數代碼一樣的，求大神指點

public?void?start()?{
????mWhiteArray.clear();
????mBlackArray.clear();
????isGameOver?=?false;
????mWhiteWinner?=?false;
????invalidate();
????System.exit(0);

}

???public?class?Exit?extends?AppCompatActivity?{
???private??Yard?yard;
????@Override
???protected?void?onCreate(Bundle?savedInstanceState)?{
???????super.onCreate(savedInstanceState);
???????setContentView(R.layout.top_window_exit);
???????Button?againButton2?=?(Button)?findViewById(R.id.againButton2);
???????againButton2.setOnClickListener(mAgainOnClickListener2);
???????yard?=?(Yard)?findViewById(R.id.wuziqi);

???}
???private?View.OnClickListener?mAgainOnClickListener2?=?new?View.OnClickListener()?{
???????@Override
???????public?void?onClick(View?v)?{
??????????yard.start();
???????}
???};
}