android.annotation.Nullable not

报上面错误是没找到包文件可以改成下面这两行

import android.support.v4.util.Pools;
import javax.annotation.Nullable;

报上面错误是没找到包文件可以改成下面这两行

import android.support.annotation.Nullable;

没找到包文件可以去查找相应的包文件有没有存在，或者是目录名字顺序错误

https://blog.csdn.net/stamsuper/article/details/79616563
https://blog.csdn.net/taoerchun/article/details/90347644
https://blog.csdn.net/taoerchun/article/details/90347644
https://blog.csdn.net/koufulong/article/details/99714992
https://bbs.csdn.net/topics/392059996
https://blog.csdn.net/weixin_39306574/article/details/86716296
https://blog.csdn.net/tanlove1314/article/details/94719708
https://coding.imooc.com/learn/questiondetail/140596.html
https://www.cnblogs.com/mapleyuan/p/5302595.html
https://blog.csdn.net/qq_15110579/article/details/78978648