2.4 Java1608: polymorphism based on overloaded methods

Revised: Thu Mar 31 11:22:34 CDT 2016

This page is included in the following Books:

• ITSE 2321 - Object-Oriented Programming (Java)
• Object-Oriented Programming (OOP) with Java

Table of contents

• Preface
  • Viewing tip
    • Listings
• Preview
• Discussion and sample code
• Summary
• What's next?
• Miscellaneous
• Complete program listings

Preface

This module is one of a series of modules designed to teach you about the essence of Object-Oriented Programming (OOP) using Java.

Viewing tip

I recommend that you open another copy of this document in a separate browser window and use the following links to easily find and view the listings while you are reading about them.

Listings

• Listing 1 . Definition of the class named A.
• Listing 2 . Definition of the class named B.
• Listing 3 . Definition of the driver class named Poly01.
• Listing 4 . Complete program listing.

Preview

Previous modules introduced overloading and overriding methods. This module concentrates on the use of method overloading to achieve compile-time polymorphism .

Every class in Java is a direct or indirect subclass of the class named Object . Methods defined in the class named Object are inherited into all other classes. Inherited methods that are not declared final may be overridden to make their behavior more appropriate for objects instantiated from the new class.

Overloaded methods have the same name and different formal argument lists. They may or may not have the same return type.

Polymorphism manifests itself in Java in the form of multiple methods having the same name. This module concentrates on method overloading, sometimes referred to as compile-time polymorphism . Subsequent modules concentrate on method overriding, sometimes referred to as runtime polymorphism .

Overloaded methods may all be defined in the same class, or may be defined in different classes as long as those classes have a superclass-subclass relationship.

Discussion and sample code

Three concepts

In an earlier module, I explained that most books on OOP will tell you that in order to understand OOP, you must understand the following three concepts:

• Encapsulation
• Inheritance
• Polymorphism

I agree with that assessment.

Encapsulation and inheritance

Previous modules in this series have explained Encapsulation and Inheritance. This module will tackle the somewhat more complex topic of Polymorphism.

Overloading and overriding methods

In the modules on inheritance, you learned a little about overloading and overriding methods (you will learn more about these concepts as you progress through these modules) . This module concentrates on the use of overloaded methods to achieve compile-time polymorphism.

Real-world scenarios

The sample programs that I used in the previous modules in this series dealt with two kinds of car radios:

• Plain car radios
• Car radios having built-in tape players

I couched those programs in a real-world scenario in an attempt to convince you that encapsulation and inheritance really do have a place in the real world.