Why Use Nested Classes in C#?

Understanding the Purpose of Nested Classes in C#

In C#, nested classes are classes that are declared within other classes. While this may initially seem perplexing, there are several compelling reasons why developers might need to utilize nested classes.

Encapsulation and Access Control:

Nested classes offer enhanced encapsulation and access control. By defining a class within another, developers can restrict the accessibility of its members to only the containing class. This allows for better organization of related functionality and ensures that sensitive or restricted data remains protected.

Factory Patterns and Object Construction:

Nested classes can be effectively employed in factory patterns, where they serve as object creators. By encapsulating the object creation process within the nested class, developers can provide a centralized and controlled method of constructing instances of the outer class. This promotes maintainability and simplifies the process of creating new objects.

Code Organization and Modularity:

Nested classes facilitate better code organization and modularity. By grouping related functionality into nested classes, code becomes more structured and easier to understand. This is especially beneficial in large and complex projects where code can become overwhelming.

Example:

One practical application of nested classes can be found in the context of financial applications. The following example demonstrates how nested classes can be used in conjunction with the factory pattern to create different types of bank accounts:

public abstract class BankAccount
{
  private BankAccount() {} // prevent third-party subclassing.
  private sealed class SavingsAccount : BankAccount { ... }
  private sealed class ChequingAccount : BankAccount { ... }
  public static BankAccount MakeSavingAccount() { ... }
  public static BankAccount MakeChequingAccount() { ... }
}

By nesting the savings and chequing account classes within the BankAccount class, the code restricts the ability of third parties to create custom subclasses. This maintains control over the creation and functionality of bank account objects.

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