Object-Oriented%20Programming%20in%20Java

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Object-Oriented Programming in Java
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Object-Oriented ProgrammingOutline

• Introduction
• Superclass subclass
• protected members
• Relationship between superclass objects
  subclass objects
• Constructors Finalizers in subclasses
• Composition versus Inheritance

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Object-Oriented ProgrammingOutline ...

• Dynamic Binding Polymorphism
• final Methods Classes
• Abstract classes Concrete subclasses
• Polymorphism examples
• Creating Using Interfaces
• Type-Wrapper Classes for Primitive Types

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Introduction

• Essential features of object-oriented programming
  (OOP) versus just using objects are
• inheritance - enables reuse of classes
• polymorphism - enables flexible use of classes

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Superclasses Subclasses

• Reuse a class via inheritance when a new class is
  a refinement of it.
• Examples
• Saturn is a Heavenlybody
• Square is a Rectangle
• Rectangle is a quadralateral
• Quadralateral is a Polygon
• Polygon is a shape

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Human Being
Honest Human Being
Criminal
Organized Criminal
Free-lance Criminal
Mafia Agent
Government Agent
Burglar
Murderer
Rapist
Senator
IRS
BATF
Congressperson
DEA
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protected members

• Protected members (data methods) are accessible
  to all members in
• its class
• its subclasses
• classes in its package

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Human Being
Honest Human Being
Criminal
Organized Criminal
Free-lance Criminal
Protected data
Bribe Source
Mafia Agent
Government Agent
Burglar
Murderer
Rapist
Senator
IRS
BATF
Congressperson
DEA
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Relationship between Superclass Subclass Objects

• An object can be referred to as a the type of its
  superclass.
• Example Zapem

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Using Constructors Finalizers in Subclasses

• When constructing an object, you can invoke the
  superclass constructor to initialize its instance
  variables
• Invoke the superclass constructor, using
• super(args)
• as the first statement of the constructor.
• Example Saturn.java
• If you do not invoke super(), Java run-time
  invokes the no-argument superclass constructor to
  initialize its variables.

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Composition versus Inheritance

• Composition has a relation
• Inheritance is a relation
• Oddly, the Point, Circle example in the text
  seems precisely off the point (a Circle is not a
  Point)
• The attributes of a Circle are its center and its
  radius it has a
• center (a Point)
• radius (a double)

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Point Circle

• public class Point
• // Instance variables
• private double x, y // coordinates of the Point
• // Methods
• public Point(double X, double Y) setPoint(X,
  Y)
• public void setPoint(double X, double Y) x
  X y Y
• public double getX() return x
• public double getY() return y
• public String toString() return x ,
  y

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Point Circle ...

• public class Circle
• // Instance variables a circle has a ...
• private Point center // center of the Circle
• private double radius // radius of the Circle
• // Methods
• public Circle(double x, double y, double r)
• center new Point(x, y)
• radius r
• public double getRadius() return radius
• public double area() return Math.PIradiusradi
  us

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Dynamic Binding Polymorphism

• Consider the statement
• objectname.methodname(args)
• When this statement executes, it
• detects the type of object that objectname
  actually refers to
• invokes the appropriate version of the methodname
  method.
• Look at the draw method in the Zapem example.

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final Methods Classes

• If a method is declared final, it cannot be
  overridden in a subclass.
• A private method is implicitly final.
• A static method is implicitly final.
• If a class is declared final
• it cannot be subclassed (i.e., extended)
• all its methods are implicitly final.

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Abstract Classes Concrete Subclasses

• An abstract class is a class that is
• designed to be extended,
• not designed to construct objects.
• An example of such a class is our Roach class An
  actual roach is either a Rectangle or an Oval.
• You cannot construct objects of an abstract class.

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Abstract Classes Concrete Subclasses ...

• You declare a class abstract by using the
  abstract keyword.
• The purpose of doing so is to provide
• interface method names signatures
• implementation implement some methods
• for its extensions.
• Please see modified Zapem example.

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Polymorphism examples

• Zapem
• SolarSystem - Please see use of Heavenly body
  class, and draw move methods.
• We can add new Roach subclasses HeavenlyBody
  classes without recompiling the zapem
  SolarSystem Applets.

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Creating Using Interfaces

• Interface isnt just an idea, its a keyword!
• An interface is used instead of an abstract
  class when
• there is no implementation to inherit
• the class already extends another class.
• A modified Zapem uses an interface.
• You also have seem their use in ActionListener
  and MouseListener

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Type-Wrapper Classes for Primitive Types

• Each primitive data type has a corresponding
  wrapper class that has the same name but with the
  1st letter capitalized
• Integer, Double, Boolean,
• These classes allow you to treat their objects as
  objects
• refer to them polymorphically
• pass them call-by-reference to methods.

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Type-Wrapper Classes for Primitive Types

• Each defines some methods. E.g.
• int Integer.parseInt(String)
• Double valueOf(String)
• String toString()
• Look in the java.lang package of the Java Core
  API Specification to find out more about these
  methods.