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Questions tagged [reflection]

Reflection is the ability of a program to observe and/or modify its structure and/or behavior at runtime. Reflection is dependent on the supporting programming language - please tag the programming language being used when using this tag.

Overview

Reflection is an ability of a program to perform introspection on itself. This usually involves observing and/or modifying its structure and behavior at runtime.

From a theoretical perspective, reflection relates to the fact that program instructions are stored as data. The distinction between program code and data is a matter of how the information is interpreted, and thus is, in fact, arbitrary. Hence, a program can treat its own code as data and observe or modify it.

Caution should be used when using reflection - the modification of a program's entity during runtime can lead to hard to detect bugs which are generally severe.

Popular questions:

Language-specific implementations

Java:

C#:

Python:

Scala:

See also

24902 questions
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How to execute a private static method with optional parameters via reflection?

I have a class with a private static method with an optional parameter. How do I invoke it from another class via Reflection? There is a similar question, but it does not address static method or optional parameters. public class Foo { private…
AngryHacker
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Is it possible to get all the eigenclasses in Ruby?

Getting a list of all modules is easy in Ruby: ObjectSpace.each_object(Module).to_a However, is it possible to get a list of all eigenclasses (also known as singleton classes or metaclasses)? Or are eigenclasses invisible? I tried str =…
Andrew Grimm
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Find only non-inherited interfaces?

I am trying to perform a query on the interfaces of a class via reflection, however the method Type.GetInterfaces() returns all the inherited interfaces also. etc public class Test : ITest { } public interface ITest : ITesting { } The code…
Alex Hope O'Connor
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Pattern matching on Class[_] type?

I'm trying to use Scala pattern matching on Java Class[_] (in context of using Java reflection from Scala) but I'm getting some unexpected error. The following gives "unreachable code" on the line with case jLong def foo[T](paramType: Class[_]):…
alphageek
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Java how can I with reflection check if a field is initialized or is default value?

So, should be straight forward question. Lets say I have a class with a lot of fields like: String thizz; long that; boolean bar; How can I, with reflection, see if the fields thizz, that and bar have been initialized or left to their default…
rapadura
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How can I create a dynamic proxy in java that retains parameter annotations on methods?

I currently am trying to proxy some existing JAX/RS resources, in order to allow me to use the Hibernate Validator's method validation support. However, when I proxy my class (currently using cglib 2.2), the FormParam annotation is not present on…
Peter Hart
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Boxed Value Type comparisons

What i'm trying to achieve here is a straight value comparison of boxed primitive types. ((object)12).Equals((object)12); // Type match will result in a value comparison, ((object)12).Equals((object)12d); // but a type mismatch will not.…
johnDisplayClass
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Calling a function using reflection that has a "params" parameter (MethodBase)

I have MethodBases for two functions: public static int Add(params int[] parameters) { /* ... */ } public static int Add(int a, int b) { /* ... */ } I have a function that calls the MethodBases via a class I made: MethodBase Method; object…
Blam
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How do I create an instance from a string in C#?

I'm reading information from an XML which contains the type of an object that I need to instantiate along with it's constructor parameters. The object type is actually in another project, within a sibling namespace. (I need to create a…
Ben S
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get fields with reflection

I want to get all fields that have null values but i aint even getting any fields: [Serializable()] public class BaseClass { [OnDeserialized()] internal void OnDeserializedMethod(StreamingContext context) { …
syncis
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Java: InvocationTargetException

I am dynamically creating classes in Java and trying to invoke methods in them, however, sometimes I get a java.lang.reflect.InvocationTargetException. PageGenerator1.java (dynamically created) import java.io.PrintStream; import…
Amir Rachum
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Cast Boxed Object back to Original Type

I expect there's one of two answers to this, either impossible or extremely simple and I've overlooked the obvious Google query. The underlying issue is that I have a generic object being passed in via an EventHandler that boxes the object and…
falquan
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Class.forName() equivalent in .NET?

What is the C# way for dynamically getting the type of object and then creating new instances of it? E.g. how do I accomplish the result of following Java code, but in C#: MyClass x = (MyClass) Class.forName("classes.MyChildClass").newInstance();
mihsathe
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Multiple instances of static variables

I'm experimenting with using different classloaders to load a particular class, and see if the static variables in that class can have different instances. Basically, I'm trying to write code for what Stephen C has mentioned in this answer. Here…
AbdullahC
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How to remove a property from class at run time

Is it possible to remove a property from class at runtime, like: public Class A { public int num1 {get;set;} public int num2 {get;set;} public int num3 {get;set;} } Class A Obj = new A(); At run time I want to remove num2 from obj. Is it…
KhanZeeshan
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