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Check if a class is derived from a generic class

I have a generic class in my project with derived classes.

public class GenericClass<T> : GenericInterface<T>
{
}

public class Test : GenericClass<SomeType>
{
}

Is there any way to find out if a Type object is derived from GenericClass?

t.IsSubclassOf(typeof(GenericClass<>))

does not work.

What is reflection and why is it useful?

What is reflection, and why is it useful?

I'm particularly interested in Java, but I assume the principles are the same in any language.

Checking if a variable is defined?

How can I check whether a variable is defined in Ruby? Is there an isset-type method available?

Get a new object instance from a Type

One may not always know the Type of an object at compile-time, but may need to create an instance of the Type. How do you get a new object instance from a Type?

How do I invoke a Java method when given the method name as a string?

If I have two variables:

Object obj;
String methodName = "getName";

Without knowing the class of obj, how can I call the method identified by methodName on it?

The method being called has no parameters, and a String return value. It's a getter for a Java bean.

How to create a generic array in Java?

Due to the implementation of Java generics, you can't have code like this:

public class GenSet<E> {
    private E a[];

    public GenSet() {
        a = new E[INITIAL_ARRAY_LENGTH]; // error: generic array creation
    }
}

How can I implement this while maintaining type safety?

I saw a solution on the Java forums that goes like this:

import java.lang.reflect.Array;

class Stack<T> {
    public Stack(Class<T> clazz, int capacity) {
        array = (T[])Array.newInstance(clazz, capacity);
    }

    private final T[] array;
}

But I really don't get what's going on. Can anyone help?

Getting all types that implement an interface

Using reflection, how can I get all types that implement an interface with C# 3.0/.NET 3.5 with the least code, and minimizing iterations?

This is what I want to re-write:

foreach (Type t in this.GetType().Assembly.GetTypes())
    if (t is IMyInterface)
        ; //do stuff

Test if object implements interface

What is the simplest way of testing if an object implements a given interface in C#? (Answer to this question in Java)

How do I use reflection to invoke a private method?

There are a group of private methods in my class, and I need to call one dynamically based on an input value. Both the invoking code and the target methods are in the same instance. The code looks like this:

MethodInfo dynMethod = this.GetType().GetMethod("Draw_" + itemType);
dynMethod.Invoke(this, new object[] { methodParams });

In this case, GetMethod() will not return private methods. What BindingFlags do I need to supply to GetMethod() so that it can locate private methods?

Change private static final field using Java reflection

I have a class with a private static final field that, unfortunately, I need to change at run-time.

Using reflection I get this error: java.lang.IllegalAccessException: Can not set static final boolean field

Is there any way to change the value?

Field hack = WarpTransform2D.class.getDeclaredField("USE_HACK");
hack.setAccessible(true);
hack.set(null, true);

Get generic type of class at runtime

How can I achieve this?

public class GenericClass<T>
{
    public Type getMyType()
    {
        //How do I return the type of T?
    }
}

Everything I have tried so far always returns type Object rather than the specific type used.

How to determine if a type implements an interface with C# reflection

Does reflection in C# offer a way to determine if some given System.Type type models some interface?

public interface IMyInterface {}

public class MyType : IMyInterface {}

// should yield 'true'
typeof(MyType)./* ????? */MODELS_INTERFACE(IMyInterface);

Can you find all classes in a package using reflection?

Is it possible to find all classes or interfaces in a given package? (Quickly looking at e.g. Package, it would seem like no.)

What is the difference between instanceof and Class.isAssignableFrom(...)?

Which of the following is better?

a instanceof B

or

B.class.isAssignableFrom(a.getClass())

The only difference that I know of is, when 'a' is null, the first returns false, while the second throws an exception. Other than that, do they always give the same result?

Why would finding a type's initializer throw a NullReferenceException?

This has got me stumped. I was trying to optimize some tests for Noda Time, where we have some type initializer checking. I thought I'd find out whether a type has a type initializer (static constructor or static variables with initializers) before loading everything into a new AppDomain. To my surprise, a small test of this threw NullReferenceException - despite there being no null values in my code. It only throws the exception when compiled with no debug information.

Here's a short but complete program to demonstrate the problem:

using System;

class Test
{
    static Test() {}

    static void Main()
    {
        var cctor = typeof(Test).TypeInitializer;
        Console.WriteLine("Got initializer? {0}", cctor != null);
    }    
}

And a transcript of compilation and output:

c:\Users\Jon\Test>csc Test.cs
Microsoft (R) Visual C# Compiler version 4.0.30319.17626
for Microsoft (R) .NET Framework 4.5
Copyright (C) Microsoft Corporation. All rights reserved.


c:\Users\Jon\Test>test

Unhandled Exception: System.NullReferenceException: Object reference not set to
an instance of an object.
   at System.RuntimeType.GetConstructorImpl(BindingFlags bindingAttr, Binder bin
der, CallingConventions callConvention, Type[] types, ParameterModifier[] modifi
ers)
   at Test.Main()

c:\Users\Jon\Test>csc /debug+ Test.cs
Microsoft (R) Visual C# Compiler version 4.0.30319.17626
for Microsoft (R) .NET Framework 4.5
Copyright (C) Microsoft Corporation. All rights reserved.


c:\Users\Jon\Test>test
Got initializer? True

Now you'll notice I'm using .NET 4.5 (the release candidate) - which may be relevant here. It's somewhat tricky for me to test it with the various other original frameworks (in particular "vanilla" .NET 4) but if anyone else has easy access to machines with other frameworks, I'd be interested in the results.

Other details:

• I'm on an x64 machine, but this problem occurs with both x86 and x64 assemblies
• It's the "debug-ness" of the calling code which makes a difference - even though in the test case above it's testing it on its own assembly, when I tried this against Noda Time I didn't have to recompile NodaTime.dll to see the differences - just Test.cs which referred to it.
• Running the "broken" assembly on Mono 2.10.8 doesn't throw

Any ideas? Framework bug?

EDIT: Curiouser and curiouser. If you take out the Console.WriteLine call:

using System;

class Test
{
    static Test() {}

    static void Main()
    {
        var cctor = typeof(Test).TypeInitializer;
    }    
}

It now only fails when compiled with csc /o- /debug-. If you turn on optimizations, (/o+) it works. But if you include the Console.WriteLine call as per the original, both versions will fail.