双击退出整个应用

//双击退出程序
private long firstTime = 0;
@Override
public boolean onKeyUp(int keyCode, KeyEvent event) {
    // TODO Auto-generated method stub
    switch(keyCode)
    {
        case KeyEvent.KEYCODE_BACK:
            long secondTime = System.currentTimeMillis();
            if (secondTime - firstTime > 2000) {                                         //如果两次按键时间间隔大于2秒，则不退出
                Toast.makeText(this, "再按一次退出程序", Toast.LENGTH_SHORT).show();
                firstTime = secondTime;//更新firstTime
                return true;
            } else {
                //两次按键小于2秒时，退出应用
                Intent intent = new Intent(Intent.ACTION_MAIN);
                intent.addCategory(Intent.CATEGORY_HOME);
                intent.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
                startActivity(intent);
                android.os.Process.killProcess(android.os.Process.myPid());
            }
            break;
    }
    return super.onKeyUp(keyCode, event);
}