为啥我的会出现以下这种情况

split 和jion两个函数，为什么变量一个写在括号里，一个写在外面？

老师 我没理解 为什么 通过这种方式 会报错   不理解什么意思

为什么我用for i in range（1000000）就一直出不来结果，少写个0才能执行，差距这么大吗

为什么用requestScope.name返回model里的值？

Exception in thread "main" java.lang.NullPointerException

at java.lang.Class.forName0(Native Method)

at java.lang.Class.forName(Class.java:264)

at com.itbaizhan.JdbcTest2.main(JdbcTest2.java:32)

老师这个什么意思，照着一个一个打的完全一样咋还是报错啊

Mon Mar 27 16:22:15 GMT+08:00 2023 WARN: Establishing SSL connection without server's identity verification is not recommended. According to MySQL 5.5.45+, 5.6.26+ and 5.7.6+ requirements SSL connection must be established by default if explicit option isn't set. For compliance with existing applications not using SSL the verifyServerCertificate property is set to 'false'. You need either to explicitly disable SSL by setting useSSL=false, or set useSSL=true and provide truststore for server certificate verification.

Exception in thread "main" com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure

The last packet successfully received from the server was 1,405 milliseconds ago.  The last packet sent successfully to the server was 1,405 milliseconds ago.

at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)

at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)

at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)

at java.lang.reflect.Constructor.newInstance(Constructor.java:423)

at com.mysql.jdbc.Util.handleNewInstance(Util.java:425)

at com.mysql.jdbc.SQLError.createCommunicationsException(SQLError.java:990)

at com.mysql.jdbc.ExportControlled.transformSocketToSSLSocket(ExportControlled.java:201)

at com.mysql.jdbc.MysqlIO.negotiateSSLConnection(MysqlIO.java:4869)

at com.mysql.jdbc.MysqlIO.proceedHandshakeWithPluggableAuthentication(MysqlIO.java:1656)

at com.mysql.jdbc.MysqlIO.doHandshake(MysqlIO.java:1217)

at com.mysql.jdbc.ConnectionImpl.coreConnect(ConnectionImpl.java:2189)

at com.mysql.jdbc.ConnectionImpl.connectOneTryOnly(ConnectionImpl.java:2220)

at com.mysql.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:2015)

at com.mysql.jdbc.ConnectionImpl.<init>(ConnectionImpl.java:768)

at com.mysql.jdbc.JDBC4Connection.<init>(JDBC4Connection.java:47)

at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)

at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)

at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)

at java.lang.reflect.Constructor.newInstance(Constructor.java:423)

at com.mysql.jdbc.Util.handleNewInstance(Util.java:425)

at com.mysql.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:385)

at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:323)

at java.sql.DriverManager.getConnection(DriverManager.java:664)

at java.sql.DriverManager.getConnection(DriverManager.java:247)

at com.itbaizhan.jdbcTest.main(jdbcTest.java:15)

Caused by: javax.net.ssl.SSLHandshakeException: No appropriate protocol (protocol is disabled or cipher suites are inappropriate)

at sun.security.ssl.HandshakeContext.<init>(HandshakeContext.java:171)

at sun.security.ssl.ClientHandshakeContext.<init>(ClientHandshakeContext.java:106)

at sun.security.ssl.TransportContext.kickstart(TransportContext.java:238)

at sun.security.ssl.SSLSocketImpl.startHandshake(SSLSocketImpl.java:410)

at sun.security.ssl.SSLSocketImpl.startHandshake(SSLSocketImpl.java:389)

at com.mysql.jdbc.ExportControlled.transformSocketToSSLSocket(ExportControlled.java:186)

... 18 more

老师我的代码和课的一样可是运行结果是上面这些为什么啊

老师，直接在A的run方法里创建B的线程对象实现包装，在A类中联合，和课堂讲的区别在哪里呢

class A implements Runnable{
    @Override
    public void run() {
        Thread t3 =new Thread(new B());
        t3.start();
        for(int i=0;i<10;i++){
            if(i==5){
                try {
                    t3.join();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
            System.out.println(Thread.currentThread().getName()+":  A"+i);
            try {
                Thread.sleep(1000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }
}
class B implements Runnable{

    @Override
    public void run() {
        for(int i=0;i<20;i++){
            System.out.println(Thread.currentThread().getName()+"  B"+i);
            try {
                Thread.sleep(1000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }
}

public class TestJoinThread {
    public static void main(String[] args) {
        Thread t1 = new Thread(new A());
        t1.start();

        for(int i=0;i<10;i++){
            System.out.println(Thread.currentThread().getName()+"      "+i);
            //当主线程迭代因子为2时，并入A线程
            if(i==2){
                try {
                    t1.join();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
            try {
                Thread.sleep(1000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }
}

import re

import requests

from fake_useragent import  UserAgent

url = 'https://www.qidian.com/rank/yuepiao/'

headers = {'User-Agent':UserAgent().chrome}

res = requests.get(url,headers = headers)

res.encoding = 'utf-8'

with open('tmp.html','w',encoding='utf-8') as f:

     f.write(res.text)

rs =re.findall('<div class="book-mid-info"> <h2><a href=".+?>(.+)</a>',res.text)

print(rs)

爬的起点网，为什么会爬出来想要的东西后面的那些什么标签什么的呀

这节听到我一头雾水

两个\\为什么输出之后变成一个\了，aabb\\cc→aabb\cc?

老师，我这个是怎么回事？我看有好多人都问了，还是不太懂。我这个应该要怎么办呢？

老师，这个权限不足页面的话，我可不可以设计成当用户权限不足的时候，我直接不显示该标签，让用户直接找不到这个权限