Should i use reflection

I can safely change the behavior of this private method as I know where it is called from. Powered by GitBook. Do Not Use Reflection. Don't use Reflection Summary Do not use reflection in your code i. In such cases, you always have an answer: use reflection! You can always implement method listener by storing java.

Method instances for annotated methods and invoke them like it is implemented in many frameworks, but we decided to have a look at other options. Reflection calls have their cost, and if you develop a production-class framework, even tiny improvements may pay back in a short time. For most Java developers, reflection is not a new thing and it is used in many cases. Just think about annotation processing, data serialization, method binding via annotations, or configuration files.

For the most popular IoC frameworks, the reflection API is a cornerstone because of extensive usage of class proxying, method reference usage, etc. Also, you can add aspect-oriented programming to this list. Some AOP frameworks rely on reflection for method execution interception. Speed — reflection calls are slower than direct calls.

Type safety — if you use method reference in your code, it is just a method reference. If you write a code that invokes a method via its reference and passes wrong parameters, the invocation will fail at runtime, not at compile time or load time. Traceability — if a reflective method call fails, it might be tricky to find a line of code that caused this because stack trace is usually huge. You need to dig really deep into all these invoke and proxy calls.

But if you look into event listener implementations in Spring or JPA callbacks in Hibernate, you will see familiar java. Method references inside. And I doubt that it will be changed in the near future; mature frameworks are big and complex and used in many mission-critical systems, and because of this, developers should introduce big changes carefully. The first candidate for reflection replacement is code generation. Nowadays, we can see a rise of new frameworks like Micronaut and Quarkus that are targeted to two aims: fast start time and low memory footprint.

Those two metrics are vital in the age of microservices and serverless applications. And recent frameworks are trying to get rid of reflection completely by using ahead-of-time compilation and code generation. Ordinarily, don't. If you want to call a method, just call it. If you want to mutate a member, just declare it mutable instead of going behind the compile's back.

One useful real-world use of reflection is when writing a framework that has to interoperate with user-defined classes, where the framework author doesn't know what the members or even the classes will be. Reflection allows them to deal with any class without knowing it in advance. For instance, I don't think it would be possible to write a complex aspect-oriented library without reflection. As another example, JUnit used to use a trivial bit of reflection: it enumerates all methods in your class, assumes that all those called testXXX are test methods, and executes only those.

But this can now be done better with annotations instead, and in fact JUnit 4 has largely moved to annotations instead. I needed to invoke all of the methods in the inner class, and invoking them manually would've been too much work.

Using reflection, I could invoke all these methods in just lines of code, instead of the number of the methods themselves. Therefore, using reflection might be a good idea when your program's code is a useful source of data. But there are trade-offs, so it might not always be a good idea.

But this is a lot of boilerplate code, and everytime you change the class, you have to update the code. Really, you could describe what this code does as. This is an algorithm, and the algorithm's input is the class: we need its name, and the names, types and values of its properties. This is where reflection comes in: it gives you access to this information.

Java allows you to inspect types using the methods of the Class class. However, full reflection means not only looking at existing code which by itself is known as "introspection" , but also modifying or generating code. There are two prominent use cases in Java for this: proxies and mocks.

Now you also want some log output; you simply want a log message whenever a method is called. You could add log output to every method explicitly, but that would be annoying, and you'd have to do it twice; once for each implementation. So even more when you add more implementations. Reflection allows you to define a new class using this algorithm.

Java allows you to do this using the methods of the java. Proxy class, and there are libraries that give you even more power. Reflection allows a program to work with code that may not be present and do so in a reliable way. Reflection allow you to load classes based on their names in string form and test them for various properties useful for multiple versions outside your control before launching actual classes that depend on them.

A typical example is the OS X specific code used to make Java programs look native under OS X, which are not present on other platforms. Spring 3 onwards, you can define the dependencies using annotations as well, using autowiring. Annotations are analyzed for dependencies injection using reflection only.

ORMs like hibernate use the config files not they use annotations for defining the relationship between entities and relationship between entity and database schemas. All this information is processed using java reflection capability. If you remember the previous versions of Junit , then to run a testcase all you cad to do, was name a method starting with test e.

Junit processor was using reflection to iterate over all methods in class, and find-out methods starting with test and run this as testcase.

In later version, the naming convention to start with test was replaced with usage of annotations, but the usage of reflection is much more similar. Subscribe to get new post notifications, industry updates, best practices, and much more. Directly into your inbox, for free. Whether building applications for consumers or servers, the scalable programming language seems to pop up everywhere. This is very nice article. I have one questions.

You have mentioned that eclipse uses Reflection for auto -assist option. But reflection work on run time and auto -assist is before run time. Could you please explain how it work?