uni/year2/semester1/logseq-stuff/pages/Abstraction & Polymorphism.md

• #CT2106 - Object-Oriented Programming
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• Why use an abstract class?
  • You should use an abstract class in situations where you want to use inheritance but do not want another developer to create an object from the superclass.

• Abstract Methods

  • Abstract classes can also have abstract methods.
  • Abstract methods are methods with no body.

    • public abstract void sing();
      

    • In other words, they do nothing.
  • Abstract methods provide the definition of a method that at least one of its subclasses must implement.

• Concrete

  • The adjective concrete is often used in OOP to denote a class or method that is not abstract.
    • i.e., the class or method is fully implemented.

• Reference Type

  • An abstract class is often used as the type of a reference variable.

    • Animal animal = new Canary("bruh");
      

• Polymorphism

  • What is polymorphism? #card card-last-interval:: 3.45 card-repeats:: 2 card-ease-factor:: 2.46 card-next-schedule:: 2022-11-18T06:09:31.768Z card-last-reviewed:: 2022-11-14T20:09:31.768Z card-last-score:: 5
    • Polymorphism refers to how an object can be treated as belonging to several types as long as those types are higher than the object's type in the class hierarchy.
  • In general, a variable of type X can point to any object that has an "is-a" relationship to type X.
    • e.g., a variable of type Animal can point to a Bird, Frog, or Fish object.