Lecture Java programming language: Inheritance and Polymorphism has main content such as Object-Oriented programming, extending a class, implementing a subclass, polymorphism, abstract classes, interfaces. | Inheritance and Polymorphism Ho Dac Hung 1 Object-Oriented Programming Object-oriented programming is based on a paradigm in which objects are used to model a specification. Objects are created from classes which provide encapsulation. Inheritance extends a class and provides a mean of polymorphism. 2 Extending a Class Making one class an extension of another involves inheritance. Inheritance allows a class to define a specialized type of an already existing class. Classed that are derived from existing classes demonstrate an is-a relationship. A class is a type of another class. 3 Implementing a Subclass A class that inherits another class includes the keyword extends in the class declaration and takes the form public class extends 4 Implementing a Subclass Designing a subclass requires selecting the superclass or base class and then defining any additional variable and method members for the subclass. In many cases existing methods in the base class will also be overridden by new definition in the subclass also called the derived class. 5 Implementing a Subclass In a subclass the keyword super is used to access methods of the base class. Members that are declared private are not accessible to derived classes. Therefore accessor methods are used to get inherited member variable values. 6 Polymorphism Polymorphism is an OOP property in which objects have the ability to assume different types. In OOP polymorphism is based on inheritance. Because a subclass is derived from a superclass a superclass object can reference an object of the subclass. 7 Polymorphism Polymorphism is further demonstrated when the referenced object determines which method to execute. This is possible when a subclass overrides a supperclass method. 8 Abstract Classes An abstract class model an abstract concept. Anstract classes cannot be instantiated because they should not represent objects. They instead describe the more general details and actions of a type of object. 9 Abstract Classes .
