JAVA基础教程:深入学习反射与Person类结构设计

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资源摘要信息:"Java基础教程_反射-提供结构丰富Person类" Java反射机制是Java语言提供的一种基础功能,允许程序在运行时对自身进行检查和操作。这一机制广泛应用于各种框架和库中,如Spring、Hibernate等。反射通常和JavaBean紧密相关,JavaBean是一种特殊的Java类,遵循特定的设计模式,通过get/set方法(属性访问器)来访问其私有成员,同时这些类遵循特定的命名规范。使用反射,可以通过编程方式动态地访问和修改对象的状态。 本教程的标题提到了“提供结构丰富Person类”,这表明教程将围绕如何使用Java反射机制来创建一个功能全面的Person类。Person类通常会包含多个属性,如姓名、年龄、性别等,并提供相应的方法来访问这些属性。通过使用Java的反射API,可以在运行时动态地获取或设置这些属性的值,甚至是在类的定义尚未确定的情况下。 在Java中,反射主要通过java.lang.Class类以及java.lang.reflect包中的Field、Method和Constructor等类来实现。具体步骤包括: 1. 获取Class对象:使用Class类的静态方法forName()或者直接调用对象的getClass()方法来获取任意对象的Class对象。 2. 访问类的字段(Field):使用Field类来获取或设置对象的字段值。 3. 调用类的方法(Method):使用Method类来动态调用对象的方法。 4. 创建类的新实例(Constructor):使用Constructor类来动态创建新的实例。 Person类作为示例,可能包含以下基本结构: ```java public class Person { private String name; private int age; private String gender; // 构造方法 public Person(String name, int age, String gender) { this.name = name; this.age = age; this.gender = gender; } // 成员变量的getter和setter方法 public String getName() { return name; } public void setName(String name) { this.name = name; } public int getAge() { return age; } public void setAge(int age) { this.age = age; } public String getGender() { return gender; } public void setGender(String gender) { this.gender = gender; } // 更多的方法和逻辑可以添加到Person类中 } ``` 通过反射,可以不需要预先知道类的结构,就可以操作Person类的实例。例如,即使不知道Person类的存在,也可以通过Class类的getDeclaredFields()方法获取Person类的所有字段信息。 ```java Class<?> personClass = Class.forName("Person"); Field[] fields = personClass.getDeclaredFields(); for (Field field : fields) { // 处理每个字段,如输出字段名等 System.out.println(field.getName()); } ``` 在实际的应用中,反射主要用于框架开发、运行时类库的加载、类对象的动态创建等场景。由于反射的使用降低了代码的安全性,并且可能影响性能,因此在日常开发中应谨慎使用,尤其是在涉及到安全性和性能敏感的应用场景。开发者需要仔细评估反射带来的利弊,并在需要动态操作对象的场景下合理运用这一机制。

springboot+MyBatis连接MySql数据库遇到问题:### Error querying database. Cause: com.mysql.cj.jdbc.exceptions.CommunicationsException: Communications link failure The last packet successfully received from the server was 11,751 milliseconds ago. The last packet sent successfully to the server was 11,858 milliseconds ago. ### The error may exist in file [/app/tomcat/webapps/project/WEB-INF/classes/mapper/PersonWeekMapper.xml] ### The error may involve com.xmsme.mapper.PersonWeekMapper.selectPersonWeekList-Inline ### The error occurred while setting parameters ### SQL: SELECT count(0) FROM (SELECT WEEK.id, WEEK.sub_time, WEEK.need_thing, WEEK.plan_content, WEEK.target_content, WEEK.sub_time AS update_time, WEEK.create_time, WEEK.week_start, WEEK.user_id, WEEK.week_end, readInfo.id AS readId, readInfo.read_status AS readStatus, updateor.nick_name FROM t_person_weekly AS WEEK LEFT JOIN sys_user sUser ON sUser.user_id = WEEK.user_id LEFT JOIN t_read_info readInfo ON readInfo.business_id = WEEK.id AND readInfo.read_type = 'PER' LEFT JOIN sys_user updateor ON updateor.user_id = WEEK.update_by LEFT JOIN sys_user_role uRole ON uRole.user_id = WEEK.update_by LEFT JOIN sys_user_post uPost ON uPost.user_id = WEEK.user_id LEFT JOIN t_project_person person ON person.user_id = WEEK.user_id LEFT JOIN t_project_person Pperson ON Pperson.project_id = person.project_id WHERE 1 = 1 AND WEEK.is_del = 0 AND WEEK.draft = 'N' AND Pperson.user_id = ? GROUP BY WEEK.id) table_count ### Cause: com.mysql.cj.jdbc.exceptions.CommunicationsException: Communications link failure The last packet successfully received from the server was 11,751 milliseconds ago. The last packet sent successfully to the server was 11,858 milliseconds ago. ; Communications link failure The last packet successfully received from the server was 11,751 milliseconds ago. The last packet sent successfully to the server was 11,858 milliseconds ago.; nested exception is com.mysql.cj.jdbc.exceptions.CommunicationsException: Communications link failure The last packet successfully received from the server was 11,751 milliseconds ago. The last packet sent successfully to the server was 11,858 milliseconds ago.

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