What is the equivalent of Java's final in C#?

access-modifiers, c#, reserved-words

Solution

The `final` keyword has several usages in Java. It corresponds to both the `sealed` and `readonly` keywords in C#, depending on the context in which it is used.

Classes

To prevent subclassing (inheritance from the defined class):

Java

public final class MyFinalClass {...}

C#

public sealed class MyFinalClass {...}

Methods

Prevent overriding of a `virtual` method.

Java

public class MyClass
{
    public final void myFinalMethod() {...}
}

C#

public class MyClass : MyBaseClass
{
    public sealed override void MyFinalMethod() {...}
}

As Joachim Sauer points out, a notable difference between the two languages here is that Java by default marks all non-static methods as `virtual`, whereas C# marks them as `sealed`. Hence, you only need to use the `sealed` keyword in C# if you want to stop further overriding of a method that has been explicitly marked `virtual` in the base class.

Variables

To only allow a variable to be assigned once:

Java

public final double pi = 3.14; // essentially a constant

C#

public readonly double pi = 3.14; // essentially a constant

As a side note, the effect of the `readonly` keyword differs from that of the `const` keyword in that the `readonly` expression is evaluated at runtime rather than compile-time, hence allowing arbitrary expressions.

Problem

Original source