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

Question

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

EDIT: Sorry, I should have been clearer. I meant what is the equivalent when applied to a member variable - so it must be assigned once and only once.

Answer 1

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
{
    public sealed 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 expression is evaluated at runtime rather than compile-time, hence allowing arbitrary expressions.

Answer 2

It depends on the context.

• For a final class or method, the C# equivalent is sealed.
• For a final field, the C# equivalent is readonly.
• For a final local variable or method parameter, there's no direct C# equivalent.

Answer 3

sealed

Answer 4

http://en.csharp-online.net/CSharp_FAQ:_What_are_the_differences_between_CSharp_and_Java_constant_declarations

C# constants are declared using the const keyword for compile time constants or the readonly keyword for runtime constants. The semantics of constants is the same in both the C# and Java languages.

Answer 5

http://en.wikipedia.org/wiki/Comparison_of_Java_and_C_Sharp

SUMMARY:This is a comparison of the C# programming language with the Java programming language. As the two are both garbage-collected runtime-compiled languages with syntax derived from C and C++, there are many similarities between Java and C#.

Answer 6

Java class final and method final -> sealed. Java member variable final -> readonly for runtime constant, const for compile time constant.

No equivalent for Local Variable final and method argument final

Answer 7

What everyone here is missing is Java's guarantee of definite assignment for final member variables.

For a class C with final member variable V, every possible execution path through every constructor of C must assign V exactly once - failing to assign V or assigning V two or more times will result in an error.

C#'s readonly keyword has no such guarantee - the compiler is more than happy to leave readonly members unassigned or allow you to assign them multiple times within a constructor.

So, final and readonly (at least with respect to member variables) are definitely not equivalent - final is much more strict.