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

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

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

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.

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.

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.

As mentioned, sealed is an equivalent of final for methods and classes.

As for the rest, it is complicated.

• For static final fields, static readonly is the closest thing possible. It allows you to initialize the static field in a static constructor, which is fairly similar to static initializer in Java. This applies both to constants (primitives and immutable objects) and constant references to mutable objects.

  The const modifier is fairly similar for constants, but you can't set them in a static constructor.

• On a field that shouldn't be reassigned once it leaves the constructor, readonly can be used. It is not equal though - final requires exactly one assignment even in constructor or initializer.

• There is no C# equivalent for a final local variable that I know of. If you are wondering why would anyone need it: You can declare a variable prior to an if-else, switch-case or so. By declaring it final, you enforce that it is assigned at most once.

  Java local variables in general are required to be assigned at least once before they are read. Unless the branch jumps out before value read, a final variable is assigned exactly once. All of this is checked compile-time. This requires well behaved code with less margin for an error.

Summed up, C# has no direct equivalent of final. While Java lacks some nice features of C#, it is refreshing for me as mostly a Java programmer to see where C# fails to deliver an equivalent.

sealed