From 653c144f9a658d7b0d72d6117e81a813ebfe5116 Mon Sep 17 00:00:00 2001 From: q147258134 <25542139+q147258134@users.noreply.github.com> Date: Thu, 29 Nov 2018 14:50:34 +0800 Subject: [PATCH] =?UTF-8?q?Update=20Java=20=E5=9F=BA=E7=A1=80.md?= MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 翻译了反射的优缺点 --- notes/Java 基础.md | 18 +++++++++--------- 1 file changed, 9 insertions(+), 9 deletions(-) diff --git a/notes/Java 基础.md b/notes/Java 基础.md index 1cf3222a..00762e85 100644 --- a/notes/Java 基础.md +++ b/notes/Java 基础.md @@ -1209,19 +1209,19 @@ Class 和 java.lang.reflect 一起对反射提供了支持，java.lang.reflect - **Method** ：可以使用 invoke() 方法调用与 Method 对象关联的方法； - **Constructor** ：可以用 Constructor 创建新的对象。 -**Advantages of Using Reflection:** +**反射的优点：** +- **可扩展性** ：应用程序可以利用全限定名创建可扩展对象的实例，来使用来自外部的用户自定义类。 +- **类浏览器和可视化开发环境** ：一个类浏览器需要可以枚举类的成员。可视化开发环境（如IDE）可以从利用反射中可用的类型信息中受益，以帮助程序员编写正确的代码。 +- **调试器和测试工具** ： 调试器需要能够检查一个类里的私有成员。测试工具可以利用反射来自动地调用类里定义的可被发现的API定义，以确保一组测试中有较高的代码覆盖率。 -- **Extensibility Features** : An application may make use of external, user-defined classes by creating instances of extensibility objects using their fully-qualified names. -- **Class Browsers and Visual Development Environments** : A class browser needs to be able to enumerate the members of classes. Visual development environments can benefit from making use of type information available in reflection to aid the developer in writing correct code. -- **Debuggers and Test Tools** : Debuggers need to be able to examine private members on classes. Test harnesses can make use of reflection to systematically call a discoverable set APIs defined on a class, to insure a high level of code coverage in a test suite. -**Drawbacks of Reflection:** +**反射的缺点：** -Reflection is powerful, but should not be used indiscriminately. If it is possible to perform an operation without using reflection, then it is preferable to avoid using it. The following concerns should be kept in mind when accessing code via reflection. +尽管反射非常强大，但也不能滥用。如果一个功能可以不用反射完成，那么最好就不用。在我们使用反射技术时，下面几条内容应该牢记于心。 -- **Performance Overhead** : Because reflection involves types that are dynamically resolved, certain Java virtual machine optimizations can not be performed. Consequently, reflective operations have slower performance than their non-reflective counterparts, and should be avoided in sections of code which are called frequently in performance-sensitive applications. -- **Security Restrictions** : Reflection requires a runtime permission which may not be present when running under a security manager. This is in an important consideration for code which has to run in a restricted security context, such as in an Applet. -- **Exposure of Internals** :Since reflection allows code to perform operations that would be illegal in non-reflective code, such as accessing private fields and methods, the use of reflection can result in unexpected side-effects, which may render code dysfunctional and may destroy portability. Reflective code breaks abstractions and therefore may change behavior with upgrades of the platform. +- **性能开销** ：反射涉及了动态类型的解析，所以JVM无法对这些代码进行优化。因此，反射操作的效率要比那些非反射操作低得多。我们应该避免在经常被执行的代码或对性能要求很高的程序中使用反射。 +- **安全限制** ：使用反射技术要求程序必须在一个没有安全限制的环境中运行。如果一个程序必须在有安全限制的环境中运行，如Applet，那么这就是个问题了。 +- **内部暴露** ：由于反射允许代码执行一些在正常情况下不被允许的操作（比如访问私有的属性和方法），所以使用反射可能会导致意料之外的副作用，这可能导致代码功能失调并破坏可移植性。反射代码破坏了抽象性，因此当平台发生改变的时候，代码的行为就有可能也随着变化。 - [Trail: The Reflection API](https://docs.oracle.com/javase/tutorial/reflect/index.html)