What is the difference between const and readonly (C#) / final (Java)?

Question

Accepted Answer

These keywords all relate to values that should not be changed after a particular point, but their semantics differ significantly. In C#, const represents a compile-time constant and is implicitly static; its value must be known at compile time. readonly is normally an instance or static field that can be assigned only at declaration or in a constructor. In Java, final prevents reassignment of a variable after it has been initialized, but for object references it does not make the referenced object immutable. Therefore, final is closer to 'cannot reassign this variable' than to C# const. // C#
class Configuration
{
 public const int MaxRetries = 3;

public readonly string Environment;

public Configuration(string environment)
 {
 Environment = environment;
 }
}

// Java
class Configuration {
 static final int MAX_RETRIES = 3;

final String environment;

Configuration(String environment) {
 this.environment = environment;
 }
} C# const: compile-time constant; implicitly static. C# readonly: field can be assigned at declaration or in a constructor and then cannot be reassigned. Java final: variable/reference cannot be reassigned after initialization. A final or readonly reference does not automatically make the referenced object immutable. Immutable object design requires the object's own state to be protected from mutation. Compile-time constants can have binary compatibility implications when consumed across assemblies/modules, so public constants should be designed carefully.

What is the difference between const and readonly (C#) / final (Java)?

const, readonly and final

Scenario Questions

Follow-up Questions