The import org.cocos2dx.lib cannot be resolved

出错后，着了很多答案，都没有。最后看别人一个文章的评论中发现了以下一句：

I have fixed the error by going to Project Properties -> Java Build Path -> Source and then linking “cocos2dx/platform/android/java/src”

I use Eclipse Juno, so it might not appear on older versions.