Inheritance

Inheritance

1. Relationship between classes

   • Parent
     • Other names
       • Superclass
       • Base Class
   • Child
     • Other names
       • Subclass
       • Derived class
     • Can access the parents methods and fields that are...
     • Can overwrite the parents methods and fields that are...
   • Child inherits the methods of the parent
   • Child can add functionality that doesn't exist in the parent
   • The parent class' constructor is called when the child class is initialized, the parent class's parent is called, etc.

2. Keywords

   • extends
     • Used to extend a class
     • All Java classes automatically extend the java.lang.object class
   • super
     • Represents an instance of the direct parent class
     • The child class can use to call the parent class' overwritten or hidden members
   • final
     • Prevents a class from being extended
   • instanceof
     • Used to determine if an object is of a specified type

3. The behavior of the child class can be changed to address needs that the parent class does not (overwriting)

4. A child class can only extend one direct parent class

5. The child and parent have an "is a" relationship: the child "is a" version of the parent

6. Accessibility

   • public
   • protected
   • default (only if the same package)

7. Child classes can be "upcast": defined as the parent class' type