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Closed 11 years ago.
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What is the difference between an Instance and an Object?
What is the specific difference between an object and an instance?
An object is an instance of a class.
When you instantiate a class, the result is an object of the class type.
In short, An object is a software
bundle of related state and behavior.
A class is a blueprint or prototype
from which objects are created. An
instance is a single and unique unit
of a class.
Read this article: Class vs Object vs Instance
Related
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What is the difference between 'open' and 'public' in Kotlin?
(8 answers)
Closed 1 year ago.
I'm new at Kotlin and I'm reading the kotlin official documentation, it states the 4 differents visibility modifiers (public, private, internal, protected) furthermore it's also using the keyword OPEN to express that a class can be extended (that is its purpose). My question is, can OPEN be considered as a Visibility Modifier?
No, open is not a visibility modifier, as it does not affect visibility at all.
Instead, open affects if classes or methods can be extended/overridden and is the opposite of javas final in these cases.
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VB.NET Brackets () {} [] <>
(4 answers)
Closed 3 years ago.
When I was writing a program that manipulated Active Directory, I found I needed to extend the GroupPrincipal class, and found some code that told me how to do this.
<DirectoryRdnPrefix("CN")>
<DirectoryObjectClass("group")>
Public Class GroupPrincipalEx
Inherits DirectoryServices.AccountManagement.GroupPrincipal
Public Sub New(context As PrincipalContext)
MyBase.New(context)
End Sub
Public Sub New(context As PrincipalContext, samAccountName As String)
...
What are the parts in angle-brackets called? What are they for? Where can I learn more about them.
I'm not asking about something specific to this case, my program works just fine. I just don't know what this language feature is, or does, or when to use it in future cases.
These are Attributes. Attributes can be evaluated by using Reflection.
Attributes
Attributes provide a powerful method of associating metadata, or
declarative information, with code (assemblies, types, methods,
properties, and so forth). After an attribute is associated with a
program entity, the attribute can be queried at run time by using a
technique called reflection.
Reflection
The classes in the System.Reflection namespace, together with
System.Type, enable you to obtain information about loaded assemblies
and the types defined within them, such as classes, interfaces, and
value types. You can also use reflection to create type instances at
run time, and to invoke and access them.
I'm experimenting in Pharo and I was wondering how class, instance variable scope is achieved.
More to the point, instance variables can be accessed by all the methods of that instance of a class, also class instance variables can be accessed by all the methods of the class and so on.
Where does the depth of this scope get defined in code? Can one see where and how this takes place, Smalltalk being fully Object Oriented?
I presume you are in Pharo >= 4.0, in which case you have the so called OpalCompiler.
In OpalCompiler, the variable scope is reified (see OCAbstractScope and subclasses), the scope being used during semantic analysis of the Abstract Syntax Tree (see OCASTSemanticAnalyzer).
You now have an entry point, and should follow message senders, class refs, instance variable refs, ... from this starting point.
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Classes vs. Modules in VB.NET
(8 answers)
VB.NET What is the purpose of a class or module?
(7 answers)
Closed 9 years ago.
I have been new to Visual Basic. Why exactly do we use a module in VB.NET?
What would be a small example of a module and calling it one of the form?
A Module in VB.Net is essentially a grouping a methods and fields. These members can be accessed without qualification anywhere that the module itself is accessible. This mechanism is actually how many of the standard VB operators ChDir, ChDrive, CurDir are implemented. There is a module in the VB runtime named FileSystem which defines all of these operations
The main advantages / differences between Module and Class are the following
It's a declarative grouping of functions that aren't associated with instances of an object
It's the only way to define extension methods in VB.Net
No need for a redundant qualifier on every usage of a project helper method
No need to protect a module from accidental instantiation by the developer. It's by definition not creatable
Is there a way to make one (1) instance of an object and share that instance between different files?
For instance, I have Class "A" (created in fileA.m), and I create an instance of it in a different file (fileB.m). Now, I want to use that same instance created in fileB.m in several other files (fileC.m and fileD.m) so I can share ivar's (such as a database).
How do I do that?
You would want Class A to be a singleton. Here's a great guide to help you out with that.
You need to use a static class method as a constructor which will return a singleton instance of the object you're looking for.