android_实现点击两次返回按钮才退出程序

private long lastClickTime; //最后一次点击返回按钮的时间

@Override
public boolean onKeyDown(int keyCode, KeyEvent event) {
switch (keyCode) {
case KeyEvent.KEYCODE_BACK:
{
long time = System.currentTimeMillis();
if ( time - lastClickTime < 3000) {
finish();
}else{
ToastUtil.showShortToast("再点击一次退出程序");
}
lastClickTime = time;
return false;
}
default:
break;
}
return super.onKeyDown(keyCode, event);
}