老师，为什么饿汉式可以不加final？是不是私有属性，只要自己保证自己不多次赋值就可以了？

老师，这和代码调用私有属性__obj的时候，为啥不是以

MySingleton._obj这样的方式调用，反而是试用cls.obj呢

请问这一块是改为本机地址还是注册中心的地址

这个需要咋处理呀

t1=Thread()

老师你是怎么导入模块的

概率比显著水平小，就是小概率事件发生吗

老师，连接不上网络?

请问老师，以下两种把String 转换为int的方法有什么区别，应用场景有什么区分？

Integer i3 = Integer.valueOf("123");

Integer i4 = Integer.parseInt("123");

这个图片全面一点 老师这个怎么解决呢

41岁小白，初中毕业，感觉像是在看天书，而且视频看完了也问不出什么问题来。越来越晕了。

老师好，为什么total后面加上1或2后，变量total1和total2表示的含义仍然与total相同，这1、2到底表示什么含义呢？

/**
 * 计算100之内的累加和，所有奇数和，所有偶数和
 */
public class Sum200 {
    public static void main(String[] args) {
        int sum=0;
        int oddSum=0;
        int eveSum=0;
        for (int i=0;i<=200;i++){
            sum+=i;
        if (i%2==0){
            oddSum+=i;
        }else {
            eveSum+=i;
        }
        }
        System.out.println("总和"+sum);
        System.out.println("奇数和"+oddSum);
        System.out.println("偶数和"+eveSum);

        int a=0;
        int sum1=0;
        int oddSum1=0;
        int eveSum1=0;
        while (a<=200){
            a++;
            sum1+=a;
        if (a%2==0){
            eveSum1+=a;
        }else {
            oddSum1+=a;
        }
        }
        System.out.println("总和"+sum1);
        System.out.println("奇数和"+oddSum1);
        System.out.println("偶数和"+eveSum1);

    }
}

两种方法的结果不一样，后面这个是不是写错

"C:\Program Files\Java\jdk-16.0.1\bin\java.exe" "-javaagent:F:\IntelliJ IDEA 2021.3\lib\idea_rt.jar=59331:F:\IntelliJ IDEA 2021.3\bin" -Dfile.encoding=UTF-8 -classpath F:\校园卡管理系统\demo1\springjdbcdemo\out\production\springjdbcdemo;D:\百战程序员java\SSM框架和项目开发\Spring\软件\lib\commons-logging-1.2.jar;D:\百战程序员java\SSM框架和项目开发\Spring\软件\lib\spring-tx-5.2.7.RELEASE.jar;D:\百战程序员java\SSM框架和项目开发\Spring\软件\lib\spring-core-5.2.7.RELEASE.jar;D:\百战程序员java\SSM框架和项目开发\Spring\软件\lib\spring-jdbc-5.2.7.RELEASE.jar;D:\百战程序员java\SSM框架和项目开发\Spring\软件\lib\spring-beans-5.2.7.RELEASE.jar;D:\百战程序员java\SSM框架和项目开发\Spring\软件\lib\mysql-connector-java-5.1.48.jar;D:\百战程序员java\SSM框架和项目开发\Spring\软件\lib\spring-context-5.2.7.RELEASE.jar;D:\百战程序员java\SSM框架和项目开发\Spring\软件\lib\spring-expression-5.2.7.RELEASE.jar com.bjsxt.test.addUsersTest

Wed Jan 19 14:41:22 CST 2022 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" org.springframework.jdbc.CannotGetJdbcConnectionException: Failed to obtain JDBC Connection; nested exception is com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure

The last packet successfully received from the server was 237 milliseconds ago.  The last packet sent successfully to the server was 224 milliseconds ago.

at org.springframework.jdbc.datasource.DataSourceUtils.getConnection(DataSourceUtils.java:82)

at org.springframework.jdbc.core.JdbcTemplate.execute(JdbcTemplate.java:612)

at org.springframework.jdbc.core.JdbcTemplate.update(JdbcTemplate.java:862)

at org.springframework.jdbc.core.JdbcTemplate.update(JdbcTemplate.java:917)

at org.springframework.jdbc.core.JdbcTemplate.update(JdbcTemplate.java:927)

at com.bjsxt.dao.impl.UsersDaoImpl.insertUsers(UsersDaoImpl.java:30)

at com.bjsxt.service.impl.UsersServiceImpl.addUsers(UsersServiceImpl.java:25)

at com.bjsxt.test.addUsersTest.main(addUsersTest.java:15)

Caused by: com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure

The last packet successfully received from the server was 237 milliseconds ago.  The last packet sent successfully to the server was 224 milliseconds ago.

at java.base/jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)

at java.base/jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:78)

at java.base/jdk.internal.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)

at java.base/java.lang.reflect.Constructor.newInstanceWithCaller(Constructor.java:499)

at java.base/java.lang.reflect.Constructor.newInstance(Constructor.java:480)

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 java.base/jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)

at java.base/jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:78)

at java.base/jdk.internal.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)

at java.base/java.lang.reflect.Constructor.newInstanceWithCaller(Constructor.java:499)

at java.base/java.lang.reflect.Constructor.newInstance(Constructor.java:480)

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/java.sql.DriverManager.getConnection(DriverManager.java:677)

at java.sql/java.sql.DriverManager.getConnection(DriverManager.java:189)

at org.springframework.jdbc.datasource.DriverManagerDataSource.getConnectionFromDriverManager(DriverManagerDataSource.java:155)

at org.springframework.jdbc.datasource.DriverManagerDataSource.getConnectionFromDriver(DriverManagerDataSource.java:146)

at org.springframework.jdbc.datasource.AbstractDriverBasedDataSource.getConnectionFromDriver(AbstractDriverBasedDataSource.java:205)

at org.springframework.jdbc.datasource.AbstractDriverBasedDataSource.getConnection(AbstractDriverBasedDataSource.java:169)

at org.springframework.jdbc.datasource.DataSourceUtils.fetchConnection(DataSourceUtils.java:158)

at org.springframework.jdbc.datasource.DataSourceUtils.doGetConnection(DataSourceUtils.java:116)

at org.springframework.jdbc.datasource.DataSourceUtils.getConnection(DataSourceUtils.java:79)

... 7 more

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

at java.base/sun.security.ssl.HandshakeContext.<init>(HandshakeContext.java:172)

at java.base/sun.security.ssl.ClientHandshakeContext.<init>(ClientHandshakeContext.java:98)

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

at java.base/sun.security.ssl.SSLSocketImpl.startHandshake(SSLSocketImpl.java:434)

at java.base/sun.security.ssl.SSLSocketImpl.startHandshake(SSLSocketImpl.java:412)

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

老师我想问一下出现这个异常怎么解决呀 我找了好久没找到问题....

一定要是这样吗

这样的输出结果是正确的，但是，这样为什么不行

这个运行结构是这样的