老师没有明白（循环变量pro表示的是对象的属性名）这句话，

而且课程中的18分51秒的时候，感觉老师没有说完，就感觉一下子就跳了过去

root.config(=s1[])

老师可以和我在解释一下这一行代码的含义和用法吗

老师，我为什么没有Resource注解。。。。。。

老师，在这里输出为什么会有一个None呢？

这段代码能不能把框中的nextNode节点删除呢？我感觉没必要引入第三者吧

这个doublelinkedlist是双链表这一数据结构的名字，还是java里面实打实存在的容器啊？如果是实打实存在的容器，跟linkedlist有什么区别吗

老师，我什么我只要出现异常就会回滚，添加了no-rollback-for 出现异常也会回滚

老师你好!为什么在计算薪资总和跟平均薪资的时候要去重？薪资总和不是要把所有薪资算上的吗

Error starting ApplicationContext. To display the conditions report re-run your application with 'debug' enabled.
2021-03-17 14:15:58.981 ERROR 20832 --- [           main] o.s.boot.SpringApplication               : Application run failed

org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'userServiceImpl': Injection of @Reference dependencies is failed; nested exception is java.lang.IllegalStateException: zookeeper not connected
	at com.alibaba.spring.beans.factory.annotation.AbstractAnnotationBeanPostProcessor.postProcessPropertyValues(AbstractAnnotationBeanPostProcessor.java:146) ~[spring-context-support-1.0.6.jar:na]
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1427) ~[spring-beans-5.2.5.RELEASE.jar:5.2.5.RELEASE]
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:594) ~[spring-beans-5.2.5.RELEASE.jar:5.2.5.RELEASE]
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:517) ~[spring-beans-5.2.5.RELEASE.jar:5.2.5.RELEASE]
	at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:323) ~[spring-beans-5.2.5.RELEASE.jar:5.2.5.RELEASE]
	at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:222) ~[spring-beans-5.2.5.RELEASE.jar:5.2.5.RELEASE]
	at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:321) ~[spring-beans-5.2.5.RELEASE.jar:5.2.5.RELEASE]
	at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:202) ~[spring-beans-5.2.5.RELEASE.jar:5.2.5.RELEASE]
	at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:882) ~[spring-beans-5.2.5.RELEASE.jar:5.2.5.RELEASE]
	at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:878) ~[spring-context-5.2.5.RELEASE.jar:5.2.5.RELEASE]
	at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:550) ~[spring-context-5.2.5.RELEASE.jar:5.2.5.RELEASE]
	at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.refresh(ServletWebServerApplicationContext.java:141) ~[spring-boot-2.2.6.RELEASE.jar:2.2.6.RELEASE]
	at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:747) [spring-boot-2.2.6.RELEASE.jar:2.2.6.RELEASE]
	at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:397) [spring-boot-2.2.6.RELEASE.jar:2.2.6.RELEASE]
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:315) [spring-boot-2.2.6.RELEASE.jar:2.2.6.RELEASE]
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:1226) [spring-boot-2.2.6.RELEASE.jar:2.2.6.RELEASE]
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:1215) [spring-boot-2.2.6.RELEASE.jar:2.2.6.RELEASE]
	at com.bjsxt.consumer.UserConsumerApplication.main(UserConsumerApplication.java:10) [classes/:na]
Caused by: java.lang.IllegalStateException: zookeeper not connected
	at org.apache.dubbo.remoting.zookeeper.curator.CuratorZookeeperClient.<init>(CuratorZookeeperClient.java:83) ~[dubbo-remoting-zookeeper-2.7.6.jar:2.7.6]
	at org.apache.dubbo.remoting.zookeeper.curator.CuratorZookeeperTransporter.createZookeeperClient(CuratorZookeeperTransporter.java:26) ~[dubbo-remoting-zookeeper-2.7.6.jar:2.7.6]
	at org.apache.dubbo.remoting.zookeeper.support.AbstractZookeeperTransporter.connect(AbstractZookeeperTransporter.java:70) ~[dubbo-remoting-zookeeper-2.7.6.jar:2.7.6]
	at org.apache.dubbo.remoting.zookeeper.ZookeeperTransporter$Adaptive.connect(ZookeeperTransporter$Adaptive.java) ~[dubbo-common-2.7.6.jar:2.7.6]
	at org.apache.dubbo.configcenter.support.zookeeper.ZookeeperDynamicConfiguration.<init>(ZookeeperDynamicConfiguration.java:70) ~[dubbo-2.7.6.jar:2.7.6]
	at org.apache.dubbo.configcenter.support.zookeeper.ZookeeperDynamicConfigurationFactory.createDynamicConfiguration(ZookeeperDynamicConfigurationFactory.java:37) ~[dubbo-2.7.6.jar:2.7.6]
	at org.apache.dubbo.common.config.configcenter.AbstractDynamicConfigurationFactory.lambda$getDynamicConfiguration$0(AbstractDynamicConfigurationFactory.java:39) ~[dubbo-common-2.7.6.jar:2.7.6]
	at java.util.concurrent.ConcurrentHashMap.computeIfAbsent(ConcurrentHashMap.java:1660) ~[na:1.8.0_261]
	at org.apache.dubbo.common.config.configcenter.AbstractDynamicConfigurationFactory.getDynamicConfiguration(AbstractDynamicConfigurationFactory.java:39) ~[dubbo-common-2.7.6.jar:2.7.6]
	at org.apache.dubbo.common.config.configcenter.DynamicConfiguration.getDynamicConfiguration(DynamicConfiguration.java:223) ~[dubbo-common-2.7.6.jar:2.7.6]
	at org.apache.dubbo.config.bootstrap.DubboBootstrap.prepareEnvironment(DubboBootstrap.java:857) ~[dubbo-2.7.6.jar:2.7.6]
	at org.apache.dubbo.config.bootstrap.DubboBootstrap.startConfigCenter(DubboBootstrap.java:603) ~[dubbo-2.7.6.jar:2.7.6]
	at org.apache.dubbo.config.bootstrap.DubboBootstrap.useRegistryAsConfigCenterIfNecessary(DubboBootstrap.java:671) ~[dubbo-2.7.6.jar:2.7.6]
	at org.apache.dubbo.config.bootstrap.DubboBootstrap.initialize(DubboBootstrap.java:509) ~[dubbo-2.7.6.jar:2.7.6]
	at org.apache.dubbo.config.bootstrap.DubboBootstrap.init(DubboBootstrap.java:494) ~[dubbo-2.7.6.jar:2.7.6]
	at org.apache.dubbo.config.ReferenceConfig.init(ReferenceConfig.java:190) ~[dubbo-2.7.6.jar:2.7.6]
	at org.apache.dubbo.config.ReferenceConfig.get(ReferenceConfig.java:158) ~[dubbo-2.7.6.jar:2.7.6]
	at org.apache.dubbo.config.spring.beans.factory.annotation.ReferenceAnnotationBeanPostProcessor.getOrCreateProxy(ReferenceAnnotationBeanPostProcessor.java:274) ~[dubbo-2.7.6.jar:2.7.6]
	at org.apache.dubbo.config.spring.beans.factory.annotation.ReferenceAnnotationBeanPostProcessor.doGetInjectedBean(ReferenceAnnotationBeanPostProcessor.java:143) ~[dubbo-2.7.6.jar:2.7.6]
	at com.alibaba.spring.beans.factory.annotation.AbstractAnnotationBeanPostProcessor.getInjectedObject(AbstractAnnotationBeanPostProcessor.java:359) ~[spring-context-support-1.0.6.jar:na]
	at com.alibaba.spring.beans.factory.annotation.AbstractAnnotationBeanPostProcessor$AnnotatedFieldElement.inject(AbstractAnnotationBeanPostProcessor.java:539) ~[spring-context-support-1.0.6.jar:na]
	at org.springframework.beans.factory.annotation.InjectionMetadata.inject(InjectionMetadata.java:130) ~[spring-beans-5.2.5.RELEASE.jar:5.2.5.RELEASE]
	at com.alibaba.spring.beans.factory.annotation.AbstractAnnotationBeanPostProcessor.postProcessPropertyValues(AbstractAnnotationBeanPostProcessor.java:142) ~[spring-context-support-1.0.6.jar:na]
	... 17 common frames omitted
Caused by: java.lang.IllegalStateException: zookeeper not connected
	at org.apache.dubbo.remoting.zookeeper.curator.CuratorZookeeperClient.<init>(CuratorZookeeperClient.java:80) ~[dubbo-remoting-zookeeper-2.7.6.jar:2.7.6]
	... 39 common frames omitted

老师，这是什么错误？

<a th:class="@{${menu.url != '' && menu.url != '#'} ? ${menu.target}}" th:href="@{${menu.url == ''} ? |#| : ${menu.url}}">
   <i class="fa fa-bar-chart-o" th:class="${menu.icon}"></i>
       <span class="nav-label" th:text="${menu.menuName}">一级菜单</span> 
       <span th:class="${menu.url == '' || menu.url == '#'} ? |fa arrow|"></span>
</a>

老师，这写法是什么意思 能分析一下吗 有点没看懂 ，有没有这个的教程

-- 示例：查询雇员表中数据，每次只返回 10 条数据。
select em.*
from (select rownum rn, e.* from EMPLOYEES e) em
where em.rn between 1 and 10;

select rownum rn, e.*
from EMPLOYEES e
where rownum between 1 and 10;

我把代码改成第二段，结果是一样的，为什么要写那么麻烦？

感觉方块在画板上走得越来越慢是浏览器的问题吗？

老师，画红色部分是什么意思，还有括号里那些数字是什么意思？

为啥是o(2n)呢，如果是一个循环的话不是o(n)吗，所以即便是嵌套循环，也应该是o(n^2)啊，然后他是里面两个循环，应该是o((2n)^2)吧，昨天我那个写错了。

然后第二个问题..假设时间复杂度对了，那这个o((2n)^2)能否这样：(2n)^2=2^2 * n^2=4n^2，所以最后是o(n^2)

  那么一个完全没有经验的人需要往那方面进行学习