70分享（65）：Java中的反射

摘要：Share interests, spread happiness, increase knowledge, and leave a good future!

分享兴趣，传播快乐，增长见闻，留下美好！

亲爱的您

这里是LearningYard新学苑。

今天小编为您带来

Java中的反射

欢迎您的访问！

Share interests, spread happiness, increase knowledge, and leave a good future!

Dear you,

this is LearningYard Academy

Today I bring you this

Reflections in Java

Welcome to visit!

Java中的反射（Reflection）是一种机制，它允许程序在运行时获取类的结构信息（例如类的字段、方法、构造函数等），并能够动态地调用这些成员。反射提供了一种灵活的方式，可以在运行时操作类、对象和方法，而无需在编译时明确知道这些信息。

Reflection (Reflection) in Java is a mechanism that allows programs to obtain structural information about a class (such as its fields, methods, constructors, etc.) and to dynamically call these members. Reflection provides a flexible way to manipulate classes, objects, and methods at runtime without the explicit knowledge of this information at compile-time.

1.反射的主要功能

1. Main function of the reflex

获取类的元数据：可以在运行时获取类的构造器、方法、字段、注解等信息。

Get the metadata of the class: you can obtain the constructor, method, fields, notes and other information of the class at runtime.

动态加载类：可以根据类的名字动态加载类，而不需要在编译时就决定类的类型。

Dynamic loading class: Classes can dynamically load by the name without determining the type of class at compile time.

动态创建对象：可以通过反射动态地实例化对象，而不需要直接调用类的构造函数。

Dynamic object creation: You can dynamically instantiate objects through reflection without directly calling the constructor of the class.

动态访问对象的属性和方法：可以在运行时动态地访问和修改对象的字段和方法。

Dynamic access to properties and methods of objects: You can dynamically access and modify object fields and methods at runtime.

2.反射的应用场景

2. Application scenarios of reflection

动态代理：反射常常与动态代理（如java.lang.reflect.Proxy）一起使用，来动态地创建接口实现类。例如，JDK的代理类和Spring中的AOP（面向切面编程）都广泛使用了反射。

Dynamic agents: reflections is often associated with dynamic agents (such as java.lang.reflect. Proxy) is used together to dynamically create interface implementation classes. For example, JDK and AOP (section oriented programming) in Spring.

框架设计：很多框架（如Spring、Hibernate）都使用反射来进行依赖注入、ORM映射等操作。框架通过反射动态地获取和操作类的属性和方法。

Frame design: Many frameworks (such as Spring, Hibernate) use reflection for dependency injection, ORM mapping, and so on. The framework dynamically obtains and operates on the properties and methods of the class through reflection.

插件式开发：通过反射，可以动态加载插件，增强系统的灵活性。

Add-in development: Through reflection, plug-ins can be dynamically loaded to enhance the flexibility of the system.

测试和调试工具：反射允许在运行时动态地检查和操作对象的状态，常用于单元测试和调试工具中。

Test and debugging tools: Reflection allows the dynamic inspection and operation of the status of objects at runtime, and is commonly used in unit testing and debugging tools.

3.反射的优缺点

3. Advantages and disadvantages of reflection

优点：

Advantages：

灵活性：反射允许程序在运行时动态地获取和操作类的属性、方法等，极大增强了代码的灵活性和通用性。

Flexibility: Reflection allows programs to dynamically acquire and operate the properties and methods of the class at runtime, which greatly enhances the flexibility and versatility of the code.

动态加载：可以在运行时加载和实例化未知类型的类，这对于某些插件式的应用或框架特别有用。

Dynamic loading: classes of unknown types can be loaded and instantiated at runtime, especially useful for some plug-in applications or frameworks.

缺点：

Disadvantages：

性能开销：反射在运行时通过反射机制访问类的成员，可能导致较高的性能开销。由于反射需要进行额外的类型检查和方法查找，可能会比直接调用方法要慢。

Performance overhead: Reflection accmembers of a class through the reflection mechanism at runtime, potentially can in high performance overhead. Because the reflection requires additional type checking and method lookup, it may be slower than calling methods directly.

安全性：使用反射时，可以绕过Java的访问控制检查（如访问私有成员），可能会带来安全隐患。

Security: When using reflection, you can bypass Java's access control checks (such as access to private members), which may pose security risks.

代码复杂性：反射使得代码更加动态和灵活，但也可能导致代码更难理解和维护，增加调试的难度。

Code complexity: Reflection makes code more dynamic and flexible, but it can also make code harder to understand and maintain, increasing debugging difficulty.

4.示例代码

4. Example code

import java.lang.reflect.Field;

import java.lang.reflect.Method;

class Person {

private String name;

private int age;

public Person(String name, int age) {

this.name = name;

this.age = age;

}

private void displayInfo {

System.out.println("Name: " + name + ", Age: " + age);

}

public class ReflectionExample {

public static void main(String args) throws Exception {

// 获取Class对象

Class personClass = Class.forName("Person");

// 创建实例

Object personInstance = personClass.getDeclaredConstructor(String.class, int.class)

.newInstance("John", 25);

// 访问私有字段

Field nameField = personClass.getDeclaredField("name");

nameField.setAccessible(true);

String name = (String) nameField.get(personInstance);

System.out.println("Name from reflection: " + name);

// 调用私有方法

Method displayMethod = personClass.getDeclaredMethod("displayInfo");

displayMethod.setAccessible(true);

displayMethod.invoke(personInstance);

}

Java反射提供了强大的动态功能，可以在运行时操作类、字段、方法等内容，非常适合一些需要高度灵活性的场景。然而，使用反射时要谨慎，考虑性能、安全性和代码的可维护性。

Java reflection provides powerful dynamic capabilities to manipulate classes, fields, methods, and so on at runtime, perfect for scenarios that require high flexibility. However, use reflections with caution, considering performance, security, and maintainability of the code.

今天的分享就到这里了，

如果您对文章有独特的想法，

欢迎给我们留言。

让我们相约明天，

祝您今天过得开心快乐!

That’s all for today’s sharing.

Ifyou have a unique idea about the article,

pleaseleave us a message,

andlet us meet tomorrow.

Iwish you a nice day!

本文由learningyard新学苑原创，如有侵权，请联系我们！

翻译来源于百度翻译