Chapter 6: Inheritance

Chapter 6: Inheritance

1. The process of extending a class in OOP

2. 'extends' Keyword

   • used to extend a class in the class declaration, after class name but before parent class
   • In Java, only one inheritance allowed per class
     • Multiple inheritance can be achieved through use of interfaces

3. Accessibility

   • Subclass can access public and protected methods & fields of superclass, but not private methods
   • Can access default methods and fields if subclass and superclass are in same package

4. The 'is-a' Relationship

   • Special relationship that is formed between the subclass and superclass when you create a new class with inheritance
     • subclass is special type of superclass
     • Subclass inherits all public methods and fields of its superclass

5. Method Overriding

   • Done by writing a method in the subclass that has the same signature as a method in the parent class
     • Can override superclass's public & protected methods
     • Method Overloading
       • Creating a method in subclass with the same name but different list of arguments
     • Can override default methods when in same package
     • Cannot override a final method
   • Changing the behavior of a method in the parent class

6. Calling Superclass Constructors

   • When creating a child object, all parent classes are also instantiated
   • super keyword
     • An instance of the direct superclass of the current object

7. Calling Superclass Hidden Members

   • super keyword
     • Can access any member in the superclass that is visible to subclass
     • To call a hidden member or an overridden method in superclass

8. Type Casting

   • Upcasting
     • Assign object of type subclass to a reference variable of type superclass
     • Can cast an instance of a subclass to its parent class
   • Downcasting
     • Casting an object to a class down the inheritance hierarchy
     • Only allowed if parent class reference is already pointing to an instance of subclass

9. Final Classes

   • final keyword
     • Prevents extension of class

10. 'instanceOf' Keyword

    • Used to test if an object is of a specified type