How do the definitions and usage of interfaces differ in Go, Java, and C#?

Interfaces in Go, Java, and C# share a common goal — to describe a set of methods that a type must implement, but they differ in syntax and usage features.

• Go:

  • Interfaces are defined as a set of methods without explicit implementation.
  • A type is considered to implement an interface if it contains all the methods of the interface (implicit implementation).
  • Allows flexible composition and dynamic typing.

  type Reader interface {
      Read(p []byte) (n int, err error)
  }
  
  type File struct {}
  func (f File) Read(p []byte) (int, error) { /*...*/ }
  // File automatically implements Reader
  

• Java:

  • Interfaces are explicitly declared with the interface keyword.
  • A class must explicitly declare implements InterfaceName.
  • Interfaces can contain methods with implementations (default methods with Java 8).

  interface Reader {
      int read(byte[] p) throws IOException;
  }
  
  class File implements Reader {
      public int read(byte[] p) { /*...*/ }
  }
  

• C#:

  • Similar to Java: interfaces are explicitly declared.
  • A class or struct implements an interface via : InterfaceName.
  • Supports explicit and implicit implementation of interface methods.

  interface IReader {
      int Read(byte[] buffer);
  }
  
  class File : IReader {
      public int Read(byte[] buffer) { /*...*/ }
  }
  

Key differences:

• Go uses implicit implementation, which simplifies composition and reduces coupling.
• Java and C# require explicit declaration of interface implementation.
• Java and C# support additional features, such as default methods (Java) and explicit implementation (C#).