Virtual and abstract are almost the same. A virtual method has an implementation in the base class that can optionally be overridden, while an abstract method hasn&#39;t and *must* be overridden in a child class. Otherwise they are the same. Choosing between them depends on the situation. If you got a base implementation, you use virtual. If you don&#39;t, and you need every descendant to implement it for itself, you choose abstract.

Interface methods are implementations of a method that is declared in an interface that the class implements. This is quite unrelated to the other two. I think a method can be both virtual and interface. The advantage of interfaces is that you declare one interface (duh) that can be implemented by two totally different classes. That way, you can run the same code on two different classes, as long as the methods you&#39;d like to call are declared in an interface they share.

I have contentEditable element (can be p, div, ...) and I would like to get caret (cursor) position in it. I can normally achieve it with this piece of code:

    var position = window.getSelection().getRangeAt(0).startOffset;

This works fine while the element contains just text. But when the element contains some HTML formatting, the returned position is relative to caret position within included HTML element.

Let&#39;s assume contents of contentEditable element is this:

    AB&lt;b&gt;CD&lt;/b&gt;EF

If caret is inside `&lt;b&gt;&lt;/b&gt;`, let&#39;s say between C and D, the returned position with above code is 1 instead of 3 (counted from the begining of the contentEditable element&#39;s content)

Can anybody come up with solution to this ?

Get caret (cursor) position in contentEditable area containing HTML content

How to check whether input value is integer or float?

Suppose 312/100=3.12
Here i need check whether 3.12 is a float value or integer value, i.e., without any decimal place value.


How to check whether input value is integer or float?

What are the advantages and disadvantages of each of these?

 - interface methods
 - virtual methods
 - abstract methods

When one should choose what? What are the points one should keep in mind when making this decision?

Comparison : interface methods vs virtual methods vs abstract methods

<p>What are the advantages and disadvantages of each of these?</p>
<ul>
<li>interface methods</li>
<li>virtual methods</li>
<li>abstract methods</li>
</ul>
<p>When one should choose what? What are the points one should keep in mind when making this decision?</p>


Warning: This question is a bit heretical... religious programmers always abiding by good practices, please don&#39;t read it. :)

Does anyone know why the use of [TypedReference](http://msdn.microsoft.com/en-us/library/system.typedreference%28v=VS.80%29.aspx) is so discouraged (implicitly, by lack of documentation)?

I&#39;ve found great uses for it, such as when passing generic parameters through functions that shouldn&#39;t be generic (when using an `object` might be overkill or slow, if you need a value type), for when you need an opaque pointer, or for when you need to access an element of an array quickly, whose specs you find at runtime (using `Array.InternalGetReference`). Since the CLR doesn&#39;t even allow incorrect usage of this type, why is it discouraged? It doesn&#39;t seem to be unsafe or anything...

-------------

Other uses I&#39;ve found for `TypedReference`:

&quot;Specializing&quot; generics in C# (this is type-safe):

    static void foo&lt;T&gt;(ref T value)
    {
        //This is the ONLY way to treat value as int, without boxing/unboxing objects
        if (value is int)
        { __refvalue(__makeref(value), int) = 1; }
        else { value = default(T); }
    }

Writing code that works with generic pointers (this is *very* unsafe if misused, but fast and safe if used correctly):

    //This bypasses the restriction that you can&#39;t have a pointer to T,
    //letting you write very high-performance generic code.
    //It&#39;s dangerous if you don&#39;t know what you&#39;re doing, but very worth if you do.
    static T Read&lt;T&gt;(IntPtr address)
    {
        var obj = default(T);
        var tr = __makeref(obj);

        //This is equivalent to shooting yourself in the foot
        //but it&#39;s the only high-perf solution in some cases
        //it sets the first field of the TypedReference (which is a pointer)
        //to the address you give it, then it dereferences the value.
        //Better be 10000% sure that your type T is unmanaged/blittable...
        unsafe { *(IntPtr*)(&amp;tr) = address; }

        return __refvalue(tr, T);
    }

Writing a *method* version of the `sizeof` instruction, which can be occasionally useful:

    static class ArrayOfTwoElements&lt;T&gt; { static readonly Value = new T[2]; }

    static uint SizeOf&lt;T&gt;()
    {
        unsafe 
        {
            TypedReference
                elem1 = __makeref(ArrayOfTwoElements&lt;T&gt;.Value[0] ),
                elem2 = __makeref(ArrayOfTwoElements&lt;T&gt;.Value[1] );
            unsafe
            { return (uint)((byte*)*(IntPtr*)(&amp;elem2) - (byte*)*(IntPtr*)(&amp;elem1)); }
        }
    }

Writing a method that passes a &quot;state&quot; parameter that wants to avoid boxing:

    static void call(Action&lt;int, TypedReference&gt; action, TypedReference state)
    {
        //Note: I could&#39;ve said &quot;object&quot; instead of &quot;TypedReference&quot;,
        //but if I had, then the user would&#39;ve had to box any value types
        try
        {
            action(0, state);
        }
        finally { /*Do any cleanup needed*/ }
    }

So why are uses like this &quot;discouraged&quot; (by lack of documentation)? Any particular safety reasons? It seems perfectly safe and verifiable if it&#39;s not mixed with pointers (which aren&#39;t safe or verifiable anyway)...

--------------

Update:

Sample code to show that, indeed, `TypedReference` can be twice as fast (or more):

    using System;
    using System.Collections.Generic;
    static class Program
    {
        static void Set1&lt;T&gt;(T[] a, int i, int v)
        { __refvalue(__makeref(a[i]), int) = v; }

        static void Set2&lt;T&gt;(T[] a, int i, int v)
        { a[i] = (T)(object)v; }
    
        static void Main(string[] args)
        {
            var root = new List&lt;object&gt;();
            var rand = new Random();
            for (int i = 0; i &lt; 1024; i++)
            { root.Add(new byte[rand.Next(1024 * 64)]); }
            //The above code is to put just a bit of pressure on the GC
    
            var arr = new int[5];
            int start;
            const int COUNT = 40000000;
    
            start = Environment.TickCount;
            for (int i = 0; i &lt; COUNT; i++)
            { Set1(arr, 0, i); }
            Console.WriteLine(&quot;Using TypedReference:  {0} ticks&quot;,
                              Environment.TickCount - start);
            start = Environment.TickCount;
            for (int i = 0; i &lt; COUNT; i++)
            { Set2(arr, 0, i); }
            Console.WriteLine(&quot;Using boxing/unboxing: {0} ticks&quot;,
                              Environment.TickCount - start);
    
            //Output Using TypedReference:  156 ticks
            //Output Using boxing/unboxing: 484 ticks
        }
    }

(Edit: I edited the benchmark above, since the last version of the post used a debug version of the code [I forgot to change it to release], and put no pressure on the GC. This version is a bit more realistic, and on my system, it&#39;s more than three times faster with `TypedReference` on average.)

Why is TypedReference behind the scenes? It&#39;s so fast and safe... almost magical!

I have a config file that I need to load as part of the execution of a dll I am writing.

The problem I am having is that the place I put the dll and config file is not the &quot;current location&quot; when the app is running.

For example, I put the dll and xml file here:

&gt;D:\Program Files\Microsoft Team Foundation Server 2010\Application Tier\Web Services\bin\Plugins

But if I try to reference the xml file (in my dll) like this:

    XDocument doc = XDocument.Load(@&quot;.\AggregatorItems.xml&quot;)

then **.\AggregatorItems.xml** translates to:

&gt;C:\windows\system32\inetsrv\AggregatorItems.xml

So, I need to find a way (I hope) of knowing where the dll that is currently executing is located.  Basically I am looking for this:

    XDocument doc = XDocument.Load(CoolDLLClass.CurrentDirectory+@&quot;\AggregatorItems.xml&quot;)

How to get the location of the DLL currently executing?

Is there any way to listen to changes of a `DependencyProperty`? I want to be notified and perform some actions when the value changes but I cannot use binding. It is a `DependencyProperty` of another class.

Listen to changes of dependency property

I have a `C#` solution with several projects in `Visual Studio 2010`.
One is a test project (I&#39;ll call it &quot;*PrjTest*&quot;), the other is a `Windows Forms Application` project (I&#39;ll call it &quot;*PrjForm*&quot;).  There is also a third project referenced by PrjForm, which it is able to reference and use successfully.

*PrjForm* references *PrjTest*, and *PrjForm* has a class with a `using` statement:

    using PrjTest;

1. Reference has been correctly added
2. `using` statement is correctly in place
3. Spelling is correct
4. PrjTest builds successfully
5. PrjForm almost builds, but breaks on the `using PrjTest;` line with the error:

***The type or namespace name &#39;PrjTest&#39; could not be found (are you missing a using directive or an assembly reference?)***

I&#39;ve tried the following to resolve this:

1. Removed Resharper (since Resharper had no trouble recognizing the referenced project, I thought it might be worth a shot) 
2. Removed and re-added the reference and using statement
3. Recreated PrjForm from scratch
4. PrjForm currently resides inside the PrjTest folder, I tried moving it to an outside folder
5. Loaded the solution on a different computer with a fresh copy of `VS 2010`

I have done my homework and spent far too long looking for an answer online, none of the solutions has helped yet.

What else could I try?

The type or namespace name could not be found

Say I have the following class:

    public class ConfigItemType
    {
        public string Name { get; set; }
        public double SomeOtherThing { get; set; }
    }

and then I make a list of the following classes (`List&lt;ConfigItemType&gt; MyList`)

Now I have a method with the following signature:

    void AggregateValues(string someUnrelatedValue, params string[] listGoesHere)

How can I fit `MyList` in to the `listGoesHere` using the value in `ConfigItemType.Name` as the params string array?

I am fairly sure that Linq can do this.... but `MyList` does not have a `select` method on it (which is what I would have used).

Convert a list of objects to an array of one of the object&#39;s properties

I noticed that with the optional parameters in C# 4 if you specify an  optional parameter on an interface you ***don,t*** have to make that parameter optional on any implementing class:

    public interface MyInterface
    {
    	void TestMethod(bool flag = false);
    }
    
    public class MyClass : MyInterface
    {
    	public void TestMethod(bool flag)
    	{
    	    Console.WriteLine(flag);
    	}
    }

and therefore:

    var obj = new MyClass();    	
    obj.TestMethod(); // compiler error

    var obj2 = new MyClass() as MyInterface;
    obj2.TestMethod(); // prints false

Does anyone know why optional parameters are designed to work this way?

On one hand I suppose the ability to override any default values specified on the interfaces is useful though to be honest I&#39;m not sure if you should even be able to specify default values on the interface as that should be an implementation decision.

On the other hand, this disconnect means you can&#39;t always use the concrete class and the interface interchangeably. This of course, wouldn&#39;t be a problem if the default value is specified on the implementation, but then if you&#39;re exposing your concrete class as the interface (using some IOC framework to inject the concrete class for instance) then really there&#39;s no point having the default value as the caller will have to always provide it anyway.

Why are C# 4 optional parameters defined on interface not enforced on implementing class?

*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 &#39;true&#39;
    typeof(MyType)./* ????? */MODELS_INTERFACE(IMyInterface);

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

First of all... Sorry for this post. I know that there are many many posts on stackoverflow which are discussing multiple inheritance. But I already know that Java does not support multiple inheritance and I know that using interfaces should be an alternative. But I don&#39;t get it and see my dilemma:

I have to make changes on a very very large and complex tool written in Java. In this tool there is a data structure built with many different class objects with a linked member hierarchy. Anyway...

 - I have one class `Tagged` which has multiple methods and returns an object tag depending on the object&#39;s class. It needs members and static variables.
 - And a second class called `XMLElement` allows to link objects and in the end generate a XML file. I also need member and static variables here.
 - Finally, I have these many many data classes which nearly all should extend `XMLElement` and some of them `Tagged`.

Ok ok, this won&#39;t work since it&#39;s only possible to extend just one class. I read very often that everything with Java is ok and there is no need for having multiple inheritance. I believe, but I don&#39;t see how an interface should replace inheritance. 

 1. It makes no sense to put the real implementation in all data classes since it is the same every time but this would be necessary with interfaces (I think). 
 2.  I don&#39;t see how I could change one of my inheritance classes to an interface. I have variables in here and they have to be exactly there.

I really don&#39;t get it so please can somebody explain me how to handle this?

How can interfaces replace the need for multiple inheritance when have existing classes

Is there some shortcut that would allow me after creating method in an interface, select and jump to implementing class of that interface?

IntelliJ IDEA jump from interface to implementing class in Java

Saw the code snippet like 

    Set&lt;Record&gt; instances = new HashSet&lt;Record&gt;();

I am wondering if Hashset is a special kind of set. Any difference between them?

What&#39;s the difference between HashSet and Set?

I&#39;m developing android with SDK 2.3.3 using Eclipse IDE.
As you all know to run my app, I should generate virtual device.
From &#39;create new AVD&#39; window, I can see many targets. 
There are 2 targets for API level 10 such as &#39;android 2.3.3&#39; and Google APIs(Google Inc).
Among those targets, I&#39;m uncertain which one I should choose.

My question is what&#39;s the difference between them.

Thanks in advance
Dan

Difference between target google APIs and target android

I&#39;m pretty confused between some concepts of OOP: `virtual`, `override`, `new` and `sealed override`. Can anyone explain the differences?

I am pretty clear that if the derived class method is to be used, one can use the `override` keyword so that the base class method will be overriden by derived class. But I&#39;m not sure about `new`, and `sealed override`.

The difference between virtual, override, new and sealed override

As far as I know, both abstract methods and pure virtual functions do NOT provide any functionality ... So can we say they&#39;re both the same thing ?

Also, suppose a class (not necessarily declared as abstract) contains a number of implemented methods (not abstract or virtual), but contains a pure virtual function. Is this class then abstract ?

Are abstract methods and pure virtual functions the same thing?

I have an abstract class (I know that it will not compile this way, but it&#39;s for comprehension of what I want to do) :

    class AbstractComputation {
        public:
            template &lt;class T&gt; virtual void setData(std::string id, T data);
            template &lt;class T&gt; virtual T getData(std::string id);
    };
    
    class Computation : public AbstractComputation {
        public:
            template &lt;class T&gt; void setData(std::string id, T data);
            template &lt;class T&gt; T getData(std::string id, T data);
    };

So when I call `setData&lt;double&gt;(&quot;foodouble&quot;, data)` I want the double identified by `foodouble` (internal mechanism which is not the main concern here) to be set to the double data.

So how to do that? 

I think that there may be a mean by typing something like `virtual void setData&lt;double&gt;(std::string id, double data)` but I don&#39;t know how to do it.


C++ Virtual template method

In the following blog: http://weblogs.asp.net/scottgu/archive/2010/07/16/code-first-development-with-entity-framework-4.aspx

The blog contains the following code sample:

    public class Dinner
    {
       public int DinnerID { get; set; }
       public string Title { get; set; }
       public DateTime EventDate { get; set; }
       public string Address { get; set; }
       public string HostedBy { get; set; }
       public virtual ICollection&lt;RSVP&gt; RSVPs { get; set; }
    }
    
    public class RSVP
    {
       public int RsvpID { get; set; }
       public int DinnerID { get; set; }
       public string AttendeeEmail { get; set; }
       public virtual Dinner Dinner { get; set; }
    }

What is the purpose of using `virtual` when defining a property in a class?  What effect does it have?



Why use &#39;virtual&#39; for class properties in Entity Framework model definitions?

Can I define an abstract class without adding an abstract method?

Defining an abstract class without any abstract methods

I just start out with an example, that explains it best:

    public abstract class A{
    	static String str;
    }

    public class B extends A{
    	public B(){
    		str = &quot;123&quot;;
    	}
    }

    public class C extends A{
    	public C(){
    		str = &quot;abc&quot;;
    	}
    }

    public class Main{
    
    	public static void main(String[] args){
    		A b = new B();
    		A c = new C();
    		System.out.println(&quot;b.str = &quot; + b.str);
    		System.out.println(&quot;c.str = &quot; + c.str);
    	}
    }

This will print out:

b.str = abc

c.str = abc


But I would like a solution where each subclass that instantiate the super class, has their **own** class variable, at the same time I want to be able to reference that class variable through the identifier, or a method call, defined in the abstract super class.

So I would like the output to be: 

b.str = 123 

c.str = abc

Is that doable? 



Java: static field in abstract class

How can I force a subclass to implement a method in Ruby. There doesn&#39;t seem to be an abstract keyword in Ruby, which is the approach I would take in Java. Is there another more Ruby-like way to enforce abstract? 

Abstract Method in Ruby

Consider an example (which compiles in java)

    public abstract interface Interface {
    	public void interfacing();
    	public abstract boolean interfacing(boolean really);
    }

Why is it necessary for an interface to be &quot;declared&quot; abstract? Is there other rules that applies with an abstract interface?


----------
Finally: If `abstract` is obsolete, why is it included in Java? Is there a history for abstract interface?

Java abstract interface

Can an enum have abstract methods? If so, what is the use, and give a scenario which will illustrate this usage.

Content Type	Original Author	Original Content on Stackoverflow
Question	Nawaz	View Question on Stackoverflow
Solution 1 - C#	GolezTrol	View Answer on Stackoverflow

Comparison : interface methods vs virtual methods vs abstract methods

C# Problem Overview

C# Solutions

Solution 1 - C#

How to check whether input value is integer or float?

Get caret (cursor) position in contentEditable area containing HTML content

Attributions