加了try-catch还是报错了

老师，请问这个optional，List 指的是啥，为何要从typing里导入呢

还有这个判断遍历结束的条件如何理解呢

package com.cai;


import java.net.ConnectException;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;

/*
获取数据库连接测试类
 */
public class JdbcTest {
    public static void main(String[] args) throws ClassNotFoundException, SQLException {
        //连接Mysql数据库的URL
        String url="jdbc:mysql://127.0.0.1:3306/bjsxt";
        //连接数据库的用户名
        String name="root";
        //连接数据库的密码
        String pwd="root";

        //通过反射实现数据库驱动的加载与注册
        Class.forName("com.mysql.jdbc.Driver");
        //通过DriverManager对象获取数据库的连接对象
        Connection connection=DriverManager.getConnection(url,name,pwd);
        System.out.println(connection);
    }
}

没有找到错误，但是存在异常

del 语句删除的是栈内存a，还是把栈内存和堆内存都删除了；

栈内存和堆内存的关系是一一对应，缺一不可的吗

老师，“r”可以随便取吗？？还有as后面的 f 是什么意思？

from flask import Flask,make_response,request

app = Flask(__name__)

@app.route('/')
def index():
return 'Hello'

@app.route('/set_cookie/')
def set_cookie():
resp = make_response('设置了一个cookie')
resp.set_cookie('uname','alisa')
return resp

@app.route('/get_cookie/')
def get_cookie():
uname = request.cookies.get('uname')
return f'cookie里的内容是:{uname}'


if __name__ == "__main__":
app.run(debug=True)

老师，为什么我最后{uname}打出来是None

哪里错啦

"C:\Program Files\Java\jdk-19\bin\java.exe" "-javaagent:D:\Program Files\IntelliJ IDEA 2022.3.2\lib\idea_rt.jar=1574:D:\Program Files\IntelliJ IDEA 2022.3.2\bin" -Dfile.encoding=UTF-8 -Dsun.stdout.encoding=UTF-8 -Dsun.stderr.encoding=UTF-8 -classpath C:\Users\hkn\IdeaProjects\jdbcdemo\out\production\jdbcdemo;C:\Users\hkn\IdeaProjects\jdbcdemo\lib\mysql-connector-java-5.1.48.jar itbaizhan.Test

com.mysql.jdbc.exceptions.jdbc4.MySQLSyntaxErrorException: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'valuer(default,'hkn',21)' at line 1

at java.base/jdk.internal.reflect.DirectConstructorHandleAccessor.newInstance(DirectConstructorHandleAccessor.java:67)

at java.base/java.lang.reflect.Constructor.newInstanceWithCaller(Constructor.java:500)

at java.base/java.lang.reflect.Constructor.newInstance(Constructor.java:484)

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

at com.mysql.jdbc.Util.getInstance(Util.java:408)

at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:944)

at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3933)

at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3869)

at com.mysql.jdbc.MysqlIO.sendCommand(MysqlIO.java:2524)

at com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:2675)

at com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2465)

at com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2439)

at com.mysql.jdbc.StatementImpl.executeInternal(StatementImpl.java:829)

at com.mysql.jdbc.StatementImpl.execute(StatementImpl.java:729)

at itbaizhan.StatementTest.insertUsers(StatementTest.java:25)

at itbaizhan.Test.main(Test.java:9)

Process finished with exit code 0

老师，为什么我这边在开发环境点击我的收藏能正常运行，一到生产环境就报500呢

这几节的文档练习题答案好像很多和讲的不一样

TestFangFa {
    (String[] args) {
        ()()()()}
    (FenZhongYuexin){
        a =()(Yuexin/)(FenZhong<){
            System..println(+FenZhong++)}(FenZhong<){
            System..println(+FenZhong++)}(FenZhong<){
            System..println(+FenZhong++)}(FenZhong<){
            System..println(+FenZhong+++a/+)}{
            System..println(+FenZhong+++a+)}
       Yuexin}
}

TestFangFa {
    (String[] args) {
        ()()()()}
    (FenZhongYuexin){
        a =()(Yuexin/)(FenZhong<){
            System..println(+FenZhong++)}(FenZhong<){
            System..println(+FenZhong++)}(FenZhong<){
            System..println(+FenZhong++)}(FenZhong<){
            System..println(+FenZhong+++a/+)}{
            System..println(+FenZhong+++a+)}
       Yuexin}
}