Java reflection performance how to#
Java reflection performance code#

Poorly skilled developers simply do not get this and believe that they can be passed anything in any part of their code and do what they want from a (hard-coded) set of possibilities. You have no idea what the hell you are doing.If at any point in your code, point 2 is not valid for an object you have been passed then one or more of these is true You ensure the truth of the previous point by specifying the correct input type for every function and having each function know no more (and do no more) than is relevant.In any point of your code you should know enough about an object's type to know what relevant functions it has and ask it to call its particular version of those functions.

Java reflection performance how to#

You group functions which know how to manipulate a structure/concept with the thing itself.

The author refuses to accept that reflection is the wrong technique and accuses anybody who points this out as 'not knowing how to help me'.

The author wants to find out which type of object has been passed in and then call one of its methods.

I have lost count of how many bad questions I have seen on StackExchange sites where Use of reflection is often harmful in OO languages if not used with great awareness. Defining an interface with the appropriate method(s) and implementing it on the set of classes you want to call the method(s) on is usually sufficient to solve most simple cases. In all other cases I'd suggest figuring out an approach that avoids reflection. IDE tooling that allows a user to examine the fields/methods of an arbitrary object at runtime.

For genuine reflection use cases, e.g.

For quick prototyping or 'throwaway' code when it is the simplest solution.

I'd suggest limiting the use of reflection to the following cases: I once got a 10x speedup in some Clojure code simply by eliminating all reflection, so yes, this is a real issue.

If you're only doing reflection occasionally then it won't matter, but this can become a performance bottleneck in cases where you are making calls via reflection thousands or millions of times per second. Performance is slower - reflection at runtime is going to be slower than statically compiled method calls/variable lookups.using a hard-coded string) then this won't get changed by most code refactoring tools and you'll instantly have a bug, which might be quite hard to track down. It causes bugs when refactoring - if you are accessing a member based on its name (e.g.Even if you do catch the error, it will be be more difficult to debug. If you are using reflection, you'll get an error at runtime which might affect end users if you don't test well enough. You lose compile-time type safety - it's helpful to have the compiler verify that a method is available at compile time.

But it is usually a bad idea in production code for at least the following reasons: If you abuse it, you can turn an otherwise simple problem into a complex and ugly mess. If you learn when and how (not) to use it, it can bring you elegant and clean solutions to otherwise difficult problems. The bottom line is, like any powerful tool, reflection too can be used to shoot yourself in the foot. Now that module ceased to be a problem to us - thanks to the judicious use of reflection. Using reflection, introspection and annotations, I managed to eliminate most of the duplication, cutting down the amount of code from over 5K to below 2.4K, while making the code more robust and way easier to maintain or extend. It contained a lot of duplicated code, where of course the duplications were not exactly the same, some of them contained bugs etc. one module of our legacy web app was meant to export/import data from DB tables to Excel sheets and back.So reflection helped us put together a simple tool quickly, without much fuss, and enabled us to focus on the important part (regression testing our web app, analysing server logs, etc.) rather than the irrelevant. Without reflection, this would take hundreds of lines of code across several applications. In some cases, it can build a simple GUI dialog box out of the identified properties on the fly. The class to be initialized has specific fields, and the config loader uses reflection to match the XML element named fieldX to the appropriate field in the class, and to initialize the latter. some of our testing tools use reflection to load configuration from XML files.Two examples from our current project (Java): which makes it infeasible (difficult to maintain in the long run). Or if there is, it is just so much more complex, involving a lot of code duplication etc. If there is a better way, use that one indeed. Now, it is often not the best (cleanest, simplest, easiest to maintain) solution. No, it's not cheating - it is a way to solve problems in some programming languages.