Interface

Interface

What is an Interface

• Background
  • Interfaces were introduced to address limitations of multiple inheritance in Object-Oriented Programming
  • They provide a way to achieve Polymorphism and define contracts for classes (What is the definition of “interface” in object oriented programming, Stack Overflow, n.d.)
• Definition:
  • An interface is a programming structure that defines a contract specifying methods a class must implement
  • It describes actions an object can perform without specifying how those actions are implemented (OOP - Interfaces, Germain, n.d.)
  • An interface defines a set of abstract methods, properties, and events that implementing classes must provide (Interfaces - define behavior for multiple types - C#, Microsoft, n.d.)
• Practical uses:
  • Interfaces allow for abstraction and separation of interface from implementation (What is an interface and why are they useful?, MyTutor, n.d.)
  • They enable polymorphism by allowing different classes to be treated uniformly (PHP OOP Interfaces, W3Schools, n.d.)
  • Interfaces facilitate code reuse and make it easier to change implementations without breaking existing code (What is an interface and why are they useful?, MyTutor, n.d.)
• Common Misconceptions
  • Interfaces are not classes and cannot contain implementation code (except for default methods in some languages) (OOP - Interfaces, Germain, n.d.)
  • Interfaces are not limited to just method declarations - some languages allow constants and static methods (What is the definition of “interface” in object oriented programming, Stack Overflow, n.d.)

Examples

Java example

public interface Insurable {
   double getPremium();
}
 
public interface InterestBearing {
   double getInterestRate();
}

• All methods in an interface are implicitly public and abstract
  • They don’t have method implementations, so there’s just a semicolon
• Java does not support multiple inheritance of classes, but it supports multiple inheritance of interfaces
• Interfaces cannot have instance fields
  • Constants can be defined in interfaces, and they are implicitly public static final

Vehicle Interface

• Defines common methods like start_engine() that all vehicle classes must implement (OOP - Interfaces, Germain, n.d.)
• Allows different vehicle types (car, truck, etc.) to be treated uniformly as “Vehicles” (OOP - Interfaces, Germain, n.d.)

Animal Sound Interface

• Defines a makeSound() method implemented differently by various animal classes (PHP OOP Interfaces, W3Schools, n.d.)
• Enables polymorphic behavior when working with different animal types (PHP OOP Interfaces, W3Schools, n.d.)

Literature Review

Germain, n.d

• OOP - Interfaces
• Key points:
  • Interfaces enforce properties on objects
  • They describe actions without implementation details
  • Interfaces enable treating different classes uniformly

Microsoft, n.d

• Interfaces - define behavior for multiple types - C#
• Key points:
  • Interfaces define functionality for multiple types
  • They can include static and default implementations in some cases
  • Interfaces enable multiple inheritance-like behavior for classes

Related Concepts

• Abstract ClassObjectOrientedProgrammingAbstraction
  • Similar to interfaces but can include implementation and state
• PolymorphismObjectOrientedProgrammingInheritance
  • Interfaces enable polymorphic behavior across different classes
• Multiple InheritanceObjectOrientedProgrammingInheritance
  • Interfaces provide an alternative to multiple inheritance in some languages