Head First Java Chapter 07 summary

Inheritance.

Inheritance is creation of hierarchy of classes such that classes below the hierarchy get some features (attributes and behaviors) from classes above the hierarchy.

• Inheritance lets you guarantee that all classes grouped under a certain supertype have all the methods that the supertype has.
• When you define a supertype for a group of classes, any subclass of that supertype can be substituted where the supertype is expected.

Polymorphism.

• With polymorphism, the reference type can be a superclass of the actual object type.
• We can have polymorphic augments and return type.(Write the method arguments as a superclass type, and you can pass any subclass object at the runtime.)

Rules of overriding.

• Arguments must be the same, and return types must be compatible.
• The method can’t be less accessible.

Overloading.

• Method overloading is nothing more than having two methods with the same name and different argument list.
• The return type can be different.
• You can’t change only the return type.
• You can vary the access levels in any direction.

BULLET POINTS

• A subclass extends a superclass.
• A subclass inherits all public instance variables and methods of the superclass, but does not inherit the private instance variables and methods of the superclass.
• Inherited methods can be overridden; instance variables cannot be overridden(although they can be redefined in the subclass).
• Use the IS-A test to verify that your inheritance hierarchy is valid.
• The IS-A relationship works in only one direction.
• When a method is overridden in a subclass, and that method is invoked on an instance of the subclass, the overridden version of the method is called.
• If a class extends A, and C extends B, class B IS-A class A, and class C IS-A class B, and Class C also IS-A class A.
• Instance variable and Class has a HAS-A relationship.