Inner classes in C#

Question

Until very recently I hadnt twigged that there was a difference between a normal class, and an inner class / sub class.

What is the relationship between an instance of an inner class and an instance of its containing class, and what is the purpose of inner classes / what makes them different?

Answer 1

Unlike Java, C# - contained classes are nested. There is no relation between containing class instance and instance of contained class. Contained classes are just used in C# to control accessibility of the contained class and avoid polluting namespaces.

(Some companies have a coding standard that each class must go into it’s own file, contained classes is a way round that for small classes.)

In Java an instance (object) of an inner class has a pointer back to the outer class. This was done in Java, as it uses lots of small classes to handle event etc. C# has delegates for that.

(Contained classes were one of the experimental ideals in Java that everyone liked but did not truly prove the test of time. As C# come along a lot later, it could learn from Java what did not work well)

Answer 2

.NET does not have inner classes like Java does. It does have nested classes.

The reason why you would use them, is to control the accessibility of the class.

Answer 3

In C# there are at least 3 differences between regular classes and inner classes which can also form a relationship between an inner class and the outer class that contains it.

• Inner classes can be declared as protected, internal, protected internal, or private while normal classes cannot.
• An inner class can access the static members of the containing outer class without using that classe's name.
• When the inner class accesses an instance of the outer class, it can access that object's private members even if they are not static.

Answer 4

C# - contained classes are nested. There is no relation between containg class instance and instance of contained class.