The code has subtle changes, but the functionality is the same. Additionally, it has some advantages over traditional reflection:. Type safety — you specify method signature in LambdaMetafactory. Traceability — lambda wrapper adds only one extra call to method invocation stack trace. It makes debugging much easier. Both method references and lambdas were created and cached before test execution.
You can download the benchmark from GitHub and run the test by yourself. For JVM As you can see, the lambda-based method handlers are about 30 percent faster on average. It is a good discussion here regarding lambda-based method invocation performance.
The outcome was that classes generated by LambdaMetafactory can be inlined, gaining some performance improvement.
And it is faster than reflection because reflective calls had to pass security checks on every invocation. This benchmark is pretty anemic and does not take into account class hierarchy, final methods, etc. All the method handles are cached after the first invocation. The new architecture has made the code cleaner and more manageable, especially in case of complex UI with a lot of event handlers.
Just have a look at the simple example. Assume that you need to recalculate the order amount based on products added to this order. You have a method calculateAmount and you need to invoke it as soon as a collection of products in the order has changed.
Here is the old version of the UI controller:. Published at DZone with permission of Andrey Belyaev. See the original article here. Performance Zone. Thanks for visiting DZone today,.
Edit Profile. Sign Out View Profile. Over 2 million developers have joined DZone. Think Twice Before Using Reflection. Replacing reflection API calls can improve performance. If there is any way but reflection to do something, that's how it should be done. Reflection causes serious heartache because you lose all advantages of using a statically typed language. If you need it you need it, however even then I'd consider a pre-packaged solution like Spring or something that completely encapsulates the reflection necessary--IE: let someone else have the headaches.
I see the term "reflection" used in official Java documentation from Oracle to describe not only the ability to make changes at runtime but also the ability to see the type of an object. Not to mention that most so-called "type introspection" related classes ex: Method , Constructor , Modifier , Field , Member , basically apparently all except Class are within the java. Perhaps the concept "reflection" comprehensively includes both "type introspection" and modification at run-time?
Show 7 more comments. Sheharyar Liedman Liedman 9, 4 4 gold badges 32 32 silver badges 35 35 bronze badges. So in other words, you can create an instance out of it's qualified name and the compiler won't complain about it because say you use just a String for the class name.
Then, at run time, if that class is not present you get an exception. You kind of bypassed the compiler in this case. Would you give me some specific use case for this? I just can't picture when i would choose it. FernandoGabrieli while it is true that it is easy to create runtime errors with reflection, it is also perfectly possible to use reflection without risking runtime exceptions.
As hinted in my answer, a common use of reflection is for libraries or frameworks, which explicitly can't know the structure of the application at compile time, since they are compiled separate from the application.
Any library that uses "code by convention" is likely to use reflection, but not necessarily using magic strings. Add a comment. Array; import java. Ben Williams Ben Williams 2, 2 2 gold badges 19 19 silver badges 15 15 bronze badges. What should Callcount be set to? StackOverflowError when I ran this. Tom callCount should be set to zero. It's value is used to determine how many tabs should precede each line of output: each time dump needs to dump a "subobject", the output would print as nested in the parent.
That method proves useful when wrapped in another. StackOverflowError might be created in case of circular references, because of the unchecked recursion: buffer. Can you specifically release your code to Public Domain, pretty please? Uses of Reflection Reflection is commonly used by programs which require the ability to examine or modify the runtime behavior of applications running in the Java virtual machine.
Extensibility Features An application may make use of external, user-defined classes by creating instances of extensibility objects using their fully-qualified names. Drawbacks of Reflection Reflection is powerful, but should not be used indiscriminately. Performance Overhead Because reflection involves types that are dynamically resolved, certain Java virtual machine optimizations cannot be performed. Security Restrictions Reflection requires a runtime permission which may not be present when running under a security manager.
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. Gary Sheppard 4, 3 3 gold badges 21 21 silver badges 33 33 bronze badges.
Desmond Smith Desmond Smith 1, 9 9 silver badges 13 13 bronze badges. Pang 8, gold badges 82 82 silver badges bronze badges. Mendelt Mendelt Class metadata can be accessed through java. Nikhil Shekhar Nikhil Shekhar 4 4 silver badges 4 4 bronze badges.
Exactly how all this works is explained here Edit : After almost 1 year I am editing this answer as while reading about reflection I got few more uses of Reflection. VeKe VeKe 8, 5 5 gold badges 57 57 silver badges 67 67 bronze badges. Example: Take for example a remote application which gives your application an object which you obtain using their API Methods.
Ihor Patsian 1, 2 2 gold badges 15 15 silver badges 24 24 bronze badges. I need something similar.. An example would help me a lot as I am new to reflection concepts.. I'm confused: can't you use instanceof to determine object type at runtime?
Isuru Jayakantha Isuru Jayakantha 2 2 silver badges 3 3 bronze badges. The required classes for reflection are provided under java. Reflection gives us information about the class to which an object belongs and also the methods of that class which can be executed by using the object.
Through reflection we can invoke methods at runtime irrespective of the access specifier used with them. Reflection can be used to get information about — Class The getClass method is used to get the name of the class to which an object belongs. Advantages of Using Reflection: Extensibility Features: An application may make use of external, user-defined classes by creating instances of extensibility objects using their fully-qualified names.
Drawbacks: Performance Overhead: 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. I would add to the drawbacks " It breaks refactoring ". For me that's the main reason to avoid reflection as much as possible. So it allows us for example , to inspect the classes we have whether we have instances of them or not , correct? Why do we say "changing the program behavior" if the behavior is already there but with different code?
Why is it called "reflection"? Thanks — Fernando Gabrieli. As per my understanding: Reflection allows programmer to access entities in program dynamically. Instead, by using reflection, there is need to worry about a possibly changing class name. DeadChex 4, 1 1 gold badge 24 24 silver badges 32 32 bronze badges.
Aurelio I just want to add some point to all that was listed. It is useful at debugging. Yoon5oo 5 5 silver badges 11 11 bronze badges. Marcus Thornton Marcus Thornton 5, 5 5 gold badges 42 42 silver badges 47 47 bronze badges. From java documentation page java. Class accommodate applications such as debuggers, interpreters, object inspectors, class browsers, and services such as Object Serialization and JavaBeans that need access to either the public members of a target object based on its runtime class or the members declared by a given class It includes following functionality.
Obtaining Class objects, Examining properties of a class fields, methods, constructors , Setting and getting field values, Invoking methods, Creating new instances of objects. From this article by Dennis Sosnoski, President, Sosnoski Software Solutions, Inc and this article security-explorations pdf : I can see considerable drawbacks than uses of using Reflection User of Reflection: It provides very versatile way of dynamically linking program components It is useful for creating libraries that work with objects in very general ways Drawbacks of Reflection: Reflection is much slower than direct code when used for field and method access.
It can obscure what's actually going on inside your code It bypasses the source code can create maintenance problems Reflection code is also more complex than the corresponding direct code It allows violation of key Java security constraints such as data access protection and type safety General abuses: Loading of restricted classes, Obtaining references to constructors, methods or fields of a restricted class, Creation of new object instances, methods invocation, getting or setting field values of a restricted class.
Have a look at this SE question regarding abuse of reflection feature: How do I read a private field in Java? Summary: Insecure use of its functions conducted from within a system code can also easily lead to the compromise of a Java security mode l. Community Bot 1 1 1 silver badge. Ravindra babu Ravindra babu A way to avoid the performance problems of Reflection in some cases is to have a class Woozle examine other classes on startup to see which ones have a static RegisterAsWoozleHelper method, and invoke all such methods it finds with a callback they can use to tell Woozle about themselves, avoiding need to use Reflection while e.
Mohammed Sarfaraz Mohammed Sarfaraz 5 5 silver badges 10 10 bronze badges. Ess Kay Ess Kay 4 4 silver badges 20 20 bronze badges. This answer would be a lot better if you gave just one unusual example of generated code either from a SQL result or XML file etc. No problem. I used reflection in a windows application that dynamically generates the interface based on XML taken from a database. So basically, there is a class I created which shows the user a report.
This report has parameters such as Date from to id, or whatever else. This info is stored in xml. So first we have a report selection. Based on the report selected, the form gets the xml.
Once the xml is retrieved, it uses reflection to create a class with fields based on reflected types. Once you change to a different report, the slate is wiped clean and new fields are generated based on the xml. So its essentially a dynamic form based on reflection. So why would we want to avoid using a powerful tool that Java provides? Loss of Refactor Safety Refactoring and code analysis tools are blind to reflection. Harder Code Comprehension In the same way that Reflection makes it harder for automated tools to understand code, it also makes it harder for humans to understand code.
Reflection introduces surprises. This method is never called, I can safely delete it. No results matching " ".
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