Polymorphism

• Provides a way to write programs that process objects that share the same superclass directly or indirectly as though they are all objects of the superclass
• Enables you to hold a reference to a Chicken object or a Duck object in a variable of type Animal

Using Scanner

• A scanner is used to get input from the user
• Import Scanner package
• A scanner should be closed
• Offers many methods: next(), nextInt(), nextLine(), nextFloat(), nextLine(), nextDouble()

Abstraction

• A class can implement multiple interfaces, but it can only extend one superclass
• Enables you to write programs that process objects that share the same superclass directly or indirectly as though they are all objects of the superclass

Modifiers

• Access modifiers: public, protected, package, private
• Public: accessible within class, within package, and in subclass
• Protected: accessible within class, within package, and in subclass
• Package: accessible within class and within package
• Private: accessible within class
• Modifiers are necessary to define proper hierarchy

Inheritance

• Refers to is-a relationship between a super class and subclass
• Super class (base class, parent class) - existing top class whose members are inherited
• Subclass inherits members of the superclass
• Super class can be used to create a subclass
• Use inheritance thoughtfully as it may not apply for some is-a relationships

Inheritance Example

• In Class Demo / Practice

Constructor Chaining

• For an instance of a class to be constructed, the compiler invokes constructors of all the superclasses along the inheritance chain
• Super() or super(arguments) must be the first statement of the subclass's constructor

Polymorphism

• Existing in many forms
• Idea: Program in the general rather than program in the specific
• Writing programs to objects that share the same superclass directly or indirectly as though they are all objects of the superclass
• A variable of a supertype can refer to a subtype object
• Method displayObject() takes a parameter of the GeometricObject type
• You can invoke displayObject() by passing any instance of GeometricObject

UML - Inheritance

• Superclass => GeometricShape
• Subclass => Circle
• Public class Circle extends GeometricShape
• Superclass fields can only be accessed by calling superclass setters and getters or via constructor

UML - Inheritance Example

• Subclass extends superclass
• Public class Rectangle extends GeometricShape {}
• The keyword extends makes Rectangle class to inherit from GeometricShape class
• Methods getColor, setColor, isFilled, setFilled, and toString can be inherited from superclass