uni/year2/semester1/logseq-stuff/pages/Interfaces.md

• #CT2106 - Object-Oriented Programming
• Previous Topic: Abstraction & Polymorphism
• Next Topic: Static Fields & Exceptions
• Relevant Slides:

• Multiple Inheritance

  • What is multiple inheritance? #card card-last-interval:: 3.05 card-repeats:: 2 card-ease-factor:: 2.6 card-next-schedule:: 2022-11-17T21:22:31.707Z card-last-reviewed:: 2022-11-14T20:22:31.708Z card-last-score:: 5
    • Multiple inheritance is where a class has multiple simultaneous superclasses.
    • However, Java does not support multiple inheritance as it has led to major problems in OOP due to conflicting field & method implementations inherited from superclasses.

• Interface

  • What is an interface? #card card-last-interval:: 3.05 card-repeats:: 2 card-ease-factor:: 2.6 card-next-schedule:: 2022-11-17T21:25:49.658Z card-last-reviewed:: 2022-11-14T20:25:49.659Z card-last-score:: 5
    • Java uses a structure called an interface to achieve a form of multiple inheritance.
      • An interface is like a class, but it is really more like ==an outline of what methods a class should have.==
    • Like a class, an interface can be used as a type.
    • By convention, interface names often end in -able.
    • While a class can only extend one super class (direct inheritance), a class can implement multiple interfaces.

  • Examples

    • public interface Eatable
      {
        public int getCalories();	// note: method definitions have no body
        public int extractEnergy;
      }
      

    • public class Canary extends Bird implements Food, Comparable() ....
      

  • What does it mean if a class implements an interface? #card card-last-interval:: 0.98 card-repeats:: 1 card-ease-factor:: 2.36 card-next-schedule:: 2022-11-15T15:21:59.543Z card-last-reviewed:: 2022-11-14T16:21:59.544Z card-last-score:: 3
    • 1. Any class that implements said interface can be treated as that interface's type (polymorphism).
      2. Any class that implements that interface must provide concrete implementations of its method.

  • Interface VS Abstract

    • Similarities

      • Both can be used to provide "templates" for what subclasses can implement.
      • An abstract method plays the same role as an interface method - both must be implemented in concrete form by a subclass.
      • An abstract class and an Interface can be used as the type for a reference variable.

    • DIfferences

      • An abstract class is used for class inheritance purposes - providing an abstract structure that subclasses inherit. Therefore, the subclasses have a lot in common.
      • However, an interface is often used to impose common functionality on classes that have nothing in common.