點兩次back鍵退出程序

private static Boolean isExit = false;
private static Boolean hasTask = false;
Timer tExit = new Timer();

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

TimerTask task = new TimerTask() {
@Override
public void run() {
isExit = false;
hasTask = true;
}
};

public boolean onKeyDown(int keyCode, KeyEvent event) {
// TODO Auto-generated method stub
if (keyCode == KeyEvent.KEYCODE_BACK) {
// System.out.println("user back down");
if (isExit == false) {
isExit = true;
Toast.makeText(this, "再按一次退出程序", Toast.LENGTH_SHORT).show();
if (!hasTask) {
tExit.schedule(task, 2000);
}
} else {
finish();
System.exit(0);
}
}
return false;
}